337-354 J. Physiol. AJ Buller and DM Lewis skeletal muscle tetanic contractions of mammalian fast

21 Pages·2006·1.93 MB·English

The rate of tension development in isometric
tetanic contractions of mammalian fast and slow
skeletal muscle

A. J. Buller and D. M. Lewis

J. Physiol. 1965;176;337-354
The Journal of Physiology Online is the official journal
of The Physiological Society. It has been published
continuously since 1878. To subscribe to The Journal of
Physiology Online go to:
http://jp.physoc.org/subscriptions/. The Journal of
Physiology Online articles are free 12 months after
publication. No part of this article may be reproduced
without the permission of Blackwell Publishing:
[email protected]
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
This information is current as of March 5, 2008
This is the final published version of this article; it
is available at:
http://jp.physoc.org

This version of the article may not be posted on a
public website for 12 months after publication
unless article is open access.
The Journal of Physiology Online is the official journal
of The Physiological Society. It has been published
continuously since 1878. To subscribe to The Journal of
Physiology Online go to:
http://jp.physoc.org/subscriptions/. The Journal of
Physiology Online articles are free 12 months after
publication. No part of this article may be reproduced
without the permission of Blackwell Publishing:
[email protected]
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
J. Phy8iol. (1965), 176, pp. 337-354 337
With 8 text-ffgure8
Printed in Great Britain
THE RATE OF TENSION DEVELOPMENT IN ISOMETRIC
TETANIC CONTRACTIONS OF MAMMALIAN FAST
AND SLOW SKELETAL MUSCLE
ByA. J. BULLER AND D. M. LEWIS
From the Physiology Department, King's College, London
(Received 8 June 1964)
Followingthedemonstration by Buller, Eccles & Eccles (1960b) thatthe
speed ofcontraction ofmammalian skeletal muscles was at least partially
determined by the motor nerve innervation, two central problems re-
mained. First, what part or parts of the contractile machinery of the
muscleareinfluenced bythe motorinnervation,and, secondly, howdo the
motoneurones bring about their influence upon the muscle fibres? The
solution ofthe first ofthese two questions requires a more detailed study
ofthecontractile mechanism ofmammalianmusclethanhashitherto been
made,withparticularattentiontoanydifferenceswhichexistbetweenfast
and slow skeletal muscle. In the mammal, both the fast and slow skeletal
muscles consist of twitch fibres, and both types of muscle are therefore
comparable with the fast fibre system ofthe frog. Onlyvery recently has
there been a demonstration ofthe equivalent ofthe frog slow fibre system
in mammalian muscles, andas yet such fibres have only beenidentified in
extrinsic ocular muscles (Hess & Pilar, 1963).
The present paper is concerned with an investigation into the rate of
isometric tension development in mammalian fast and slow muscles
following repetitive stimulation of their motor nerves. This study was a
necessary preliminary to the understanding ofthe alterations which occur
in the rate oftension development following operative cross union ofthe
nerves tomammalian fast andslow muscle (Buller &Lewis, 1964, 1965b).
A preliminary account of some of the experiments herein reported has
already been published (Buller & Lewis, 1963a).
METHODS
Theexperimentswereperformedoncatsweighing between 1-8and 2-8kganaesthetized
with pentobarbitone sodium (Nembutal). An initial dose of40mg/kgwas injected intra-
peritoneally, andanaesthesiawasmaintainedbysubsequentintravenousinjectionsthrough
ajugularcannula. Aftermakinganincisiondownthemidline ofthecalf,themusclestobe
studiedweredissectedfreefromsurroundingstructureswhilststillpreservingtheirfullblood
supply.Whileotherhind-limbmuscleshavebeenexaminedthispaperwillconfineitselftoa
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
338
A. J. BULLER AND D. M. LEWIS
comparison of the soleus and flexor hallucis longus muscle. This latter muscle is more
correctly called the mesial head ofthe flexor digitorum loingus (Chin,Cope& Pang, 1962),
since in the catitstendonofinsertionfuseswiththat ofthe largerflexordigitorum longus.
Inthispaper, however, weshall retainthe commoner terminology offlexorhallucis longus
(F.H.L.). SoleusandF.H.L.muscleswerechosenbecausetheyaretheslowestandfastestcon-
tracting calf muscles respectively and because, in any one cat, their maximum tetanic
tensionsrarely differ bymorethan 30 O0. Theindividualmotornervestothemusclesto be
usedwere carefully dissected to allowanample lengthforstimulation. Theywere then cut
centrally and thedistal ends prepared formounting onbipolar stimulating electrodes. The
individual muscle tendons were very firmly tied to steel hooks which could be attached
directly to the strain gauge. The length oftendon betweein the muscle and hook was in-
tentionally kept short. This is important, because the 'available' length of tendon for a
musclesuchas F.H.L. ismuchgreaterthanforamusclelikesoleus, andtheincorporationof
alonglength (- 2cm) oftendonintherecording systemintroduces anappreciable distor-
tion. The total compliance ofthe recording system (shortlength oftendon, steelhook and
straingauge)wastypically05mm/kg, andtheintroductionof2cmoftendonchangedthis
figureto 3mm/kg. Thesefiguresindicate onlythatpartofthetotalcompliance overwhich
theexperimenterhassomecontrol. Ittakesnoaccountoftheintramuscular tendonorthe
serieselasticelementswithinthemusclefibres. Inordertostabilizetheleg,steeltwistdrills
wereinserted into bothends ofthetibiaandthenmountedinchuckswhichweremagneti-
cally anchored to amassive metal table uponwhich all the associated equipmentwas also
located. The skin flaps formed by the primaryincisionwere sewn back tometal supports,
thus creating a pool of some 50-200ml. capacity which was filled with warmed liquid
paraffin. Oncefilled,thetemperatureofthisparaffinpoolwasmaintainedbetween36-5and
37.50 C by means ofheaters and even temperature distribution ensured by stirring. Care
was taken to see that the muscles were always fully immersed in the paraffin. On those
occasionswhenatendonwas outofthepoolduringrecording itwas coveredwith awisp of
cotton-wool soaked in paraffin. In addition the cat's body temperature was continually
monitored and the reading used to regulate the current supplied to an electric blanket on
whichthe catrested. The deviceusedwas similartothatdescribedbyKrnjevic' & Mitchell
(1961). Inordertoallowaccessforthestraingaugetheposteriorpartofthecalcaneumwas
excised and the cat's foot fixed in maximum dorsiflexion.
The master stimulator (Digitimer, Devices Ltd.) allowed the programming ofup to five
pulses separated by individually variable intervals during each oscillograph sweep. Each
pulse could be used to initiate a single stimulus, or any two pulses could be used to gate
atetanictrainofpulses,thetrainstartingsynchronouslywiththefirstofthetwopulsesand
stoppingatthesecond. Thefrequencyofthetetanictrainwascontrolledbyaseparateunit,
the fixed frequenciesavailable ranging from 1 to 1000pulses/sec. The calibrationaccuracy
was determined bya 10kc quartz crystal. Allpulseswhether singleor repetitivewere fed
tothenervethroughatransistorized stimulusisolationunit. Foreachinputpulsethisunit
provided an earth-free output pulse variable in duration and intensity. The output impe-
dance ofthe stimulus isolation unit was 500ohms. The stimuli were applied to the nerve
through platinum or silver-wire electrodes.
Recording. (a) Mlechanical. IsometrictensionwasmeasuredbymeansofeitherStathamor
Langham Thompson unbonded wire strain gauge bridges. The particulartransducerused
dependedonthesizeofthecatandwaseither G1 64orG 1 80(Statham)orUF2(Langham
Thompson).Thesegaugeshadtensionmaximaof1-9, 2-4and4-8kgandmeasuredunloaded
natural frequencies of approximately 720, 840 and 1100c/s respectively. All gauges were
d.c. excited (15-20 V) and had measured non-linearities ofless than +1% full scale.
Calibrations were obtained by shunting one of the arms of the transducer bridge with
precision resistors (0-1 %Alma). Theaccuracyofsuchcalibrationswasperiodicallychecked
byloadingthevariousstraingaugeswithweights. Thevoltageoutputfromthestraingauge
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
ISOMETRIC TETANI OF MAMMALIAN MUSCLES 339
was amplified initially by a d.c. differential amplifier, subsequently by a d.c. single-sided
amplifier, the output ofwhich wasthen displayed on one beam ofa doublebeamcathode
ray oscilloscope (Tektronix 502). The frequency response ofthe amplifier system was flat
within3dbto 1 kc/s.Thetotalnoiseofthesystemwastypicallysuchthataneasilyobserved
deflexionofthebaselinecouldbeproducedbyaforceof0-1%ofthestraingaugemaximum.
Muchmorecommonly,however,thegainoftheamplifierwasreducedsothatlargertensions
wererecordedintheapparent absence ofnoise. Bymeansofassociatedcircuitrydescribed
inmoredetailelsewhere (Buller & Lewis, 1965a), theinitial tension onthemuscle andthe
peakactivetensiondevelopedbythemuscleduringeachcontractioncouldbereaddirectly
frommeters. Inaddition, provision wasmadefortheelectrical quasi-differentiation ofthe
tension record. This was performed as illustrated diagrammatically in Fig. 1 using a
R
12C
I I1
10
~6 ~~ ~ ~ ~ ~ ~ ~
-
4-
2 C
16 32 48 64 10msec
Volts
Fig. 1. Left top. Blockdiagram ofdifferentiator. K2W = Philbrick operational
amplifiertype K2W; C = differentiatingcondenser;R =feed-backresistor; V =
in line readout voltmeter (Solartron L.M. 901).
Left middle. Ramp input to differentiator and square wave output from dif-
ferentiator. The dotshave the same significance asin Fig. 1A.
Leftbottom. Calibrationofdifferentiator, plottingthe slope oftherampinput
measureding/msecagainstthepeakvoltageoftheoutputsquarewavemeasuredin
voltsbyvoltmeter V.
Right (A) upperbeam. Typical fastisometric twitchfromF.H.L. Lowerbeam,
digital representation of some of the contraction characteristics (see Buller &
Lewis, 1965a). Theleft-handgroupofthreedotsindicatestheinitialtensiononthe
muscle,eachdotrepresenting5g.Thenextgroupoftwenty-threedots(raisedfrom
the base line) each represent 1msec and measure the time fromthe start ofcon-
traction until the time ofpeak tension development. The next group oftwenty-
threedotseachrepresent1msec andmeasurethetimefrompeaktensionuntilthe
instantofhalfdecay.Thefinalgroupoftwenty-fourdotsmeasurethepeaktension
developed during the twitch, each dot representing 10g. (B) Upper beam same
twitch, lower beam differentiated tension record. (C) Two beams superimposed.
Uppershowingoriginal twitch, lowerelectricallyintegratedrecordofthe differen-
tiatedrecord of(B). Time scale 10, 50 and 100msec.
22 Physiol. 176
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
340 A. J. BULLER AND D. M. LEWIS
PhilbrickK2Woperationalamplifierconnectedasadifferentiator. Switchedinputcapacitors
provideddifferentiatingtimeconstantsofbetween100tusecand1msec,whilehigh-frequency
noise was reduced by adding series resistance to C (Fig. 1) and shunting R with a small
capacitance. Theadvantagesofusinganoperationalamplifierasadifferentiatorratherthan
asimpleinputRCnetworkfollowedbyavoltageamplifierprovedconsiderable (cf. Korn&
Korn, 1956). The differentiator was followed by a peak-reading voltmeter and the peak
voltage developed by the differentiator was displayed on an in-line readout voltmeter
(Solartron L. M. 901). The accuracy ofthe differentiatorwas tested byelectricallyintegra-
ting the differentiated tension record (see Fig. 1). The linearity ofthepeak-reading device
wasmeasuredbyfeedingvoltagerampsequivalenttoknownratesofchangeofinputvoltage
persecond into the differentiatorandmeasuringthesquarewave voltagedevelopedbythe
differentiator (see Fig. 1). By suitable scalingthe readingofthein-line readout voltmeter
couldbeequatedto changes oftension (measureding/msec) attheinput ofanyoneofthe
strain gauges used. Ifrequired the output ofthe differentiator could be displayed on one
beam ofthe oscilloscope.
(b) Electrical. Action potentials from muscle were recorded either by means of belly
tendonleadsofsilverwireorbymeansofbipolarconcentricneedleelectrodes. Ineithercase
the signals were fed to a conventional a.c. coupled preamplifier (Tektronix 122) with 3db
pointsat 80c/s and 10kc/s. Theoutputfromthepreamplifierwas a.c. coupled (O I,uFand
1 MQ) into a Tektronix 502 oscilloscope.
Timetraceswerederivedfromcount-downcircuitsdrivenfroma10kc/scrystaloscillator.
Permanentrecordswereobtainedbyphotographingthefaceofthecathoderaytubeonfilm
(Ilfordtype 5B62) using a camera systemwith an optical reduction ofapproximately 1:3.
Thedissection completed, the catwas setup andthepoolformed. Theanimalwas then
leftforhalftoonehourforthemusclestocomeintotemperatureequilibriumwiththeparaf-
fin in the pool, since despite efforts to the contrary the muscles often cooled during
the dissection. After this the motor nerve of the muscle to be studied was stimulated
approximately once every 6 or 9sec with shocks of 30 or 100gsec duration and 2-5V
intensity (approximately 3 times that necessary to produce a maximal contraction). The
lower repetition frequency was used particularly for fast muscles such as flexor hallucis
longus. This reduced to avery low level thepotentiating effects ofprevious stimuli onthe
mechanical responses. Considerable carewasthentakentoaligncorrectlythestraingauge
in the natural line ofpull ofthe muscle,and to applythat amountofinitialtension tothe
muscle which produced the maximal twitch response. The initial tensionwas adjusted by
meansofamicrometerdrivecoupledtothestraingauge.Theextremeimportanceofcareat
thisstagehasbeenstressedbyBuller, Eccles& Eccles (1960a)andinmoredetailedstudies
byBuller & Lewis (1963b). Next, evidencewas soughtforanyeffect onthemuscletwitch
ofa back response in the motor nerve fibres (Brown & Matthews, 1960; Buller & Lewis,
1963b). This was done by applying two maximal stimuli to the motor nerve separated by
intervalsrangingbetween05and1*5msecandnotingwhetheranydecreaseinthesizeofthe
mechanicalresponseoccurred. Ifsuchaneffectwasobserved (itappearedmorecommonly
inlargecatsandinsoleus) themusclewasexcludedfromthepresentstudy. Measurements
werethencommencedofeithertheeffectsoftwostimuliatvariousintervalsortheeffectsof
short tetani (100-400msec) at various frequencies. After a tetanus the motor nervewas
stimulated bysingleshocks once every 9sec until any alteration which had taken place
inthetwitchsize(post-tetanicpotentiation, Brown&vonEuler, 1938)and/orrateoftension
developmenthaddisappeared. This rarely took longer than 60sec andwaseasilyassessed
sinceboththese contraction characteristics could be directly read out on meters after
each twitch.
Usually thefrequency ofthe tetanic stimuliwas increased insteps up to amaximuim of
400-600pulses/secandinafewcasesto1000pulses/secandthenreducedthroughintermediate
frequenciestoensure thatno changeshadtakenplaceinthemuscle asaresultofthehigh-
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
ISOMETRIC TETANI OF MAMMALIAN MUSCLES 341
frequency activation. A similarprocedurewasadoptedwiththetwo-stimuli experiments.
Occasionally the frequency changes or intervals were randomized. No differences were
noted in the results obtained.
At the conclusion of the experiment the muscles used were dissected out ofthe body,
blotted'dry'withfilterpaperandweighed.Theover-alllengthofthemuscle(butexcluding
any tendon) was also measured.
Source8 of error. The finite time constant of the differentiating network and the peak
voltagecondenser(Fig. 1blockdiagram)introduceerrorsinthereadingofthemaximumrate
ofchangeoftension. However,calculationshowsthatthemaxrimumerrorproducedwiththe
highestratesofchangeencounteredwasoftheorderof-5%.Amoreimportantsourceoferror
was theoccasional deterioration ofthemusclesfollowingrepeatedtetani. The changes ob-
servedwereeffectively confinedtothefastmusclesstudiedandwereevidencedasareduced
peaktensionanddecreasedmaximuimrateoftensionriseduringthetwitchwhilethepeakte-
tanictensionandtherateofrisewerelittleaffected.Wehavenotinvestigatedthisphenomenon
in detail, but have rejected results in which the peak twitch tension fellby 15% or more
during the course of the whole experiment. Apart from these occasional exceptions the
muscles remained in excellent condition, and consistent responses could be obtained over
many hours.
Soleus F.H.L
83 12-5 32 50
25 50 80 125
100msec 10msec
Fig. 2. Genesisoftetanusforslowandfastmammalianmuscles. Ontheleftfour
tetaniofsoleusatthestimulusfrequenciesshownbeloweachrecord. Ontheright
fourtetani of F.H.L.at thefrequenciesshown. Notethedifferent sweepspeedsfor
thetwosetsofrecords. Thedotsonthelowerbeamofeachpairofrecordsindicate
the peak tension developed during the contraction shown above. Each dot is
equivalent to 20g.
RESULTS
Figure 2 illustrates the classical genesis oftetanus experiment for both
a slowly contracting skeletal muscle (soleus) and a fast contracting
skeletal muscle (flexor hallucis longus). As has been pointed out many
timespreviously (cf. Cooper & Eccles, 1930), thestimulationratenecessary
tobringaboutapparentfusionofthemechanicalresponsesishigherforthe
fast muscle (125 pulses/sec) than for the slow muscle (50 pulses/sec). The
term apparent fusion frequency is used because, although no obvious
oscillations of the tension record may be seen at the amplification used,
Ritchie (1954) has rightly stressed that the apparent fusion frequency is
22-2
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
342 A. J. BULLER AND D. M. LEWIS
dependent on the sensitivity of the recording system. If the apparently
fusedtetaniofFig. 2wereexaminedathigheramplification, oscillations at
the stimulus frequency would certainly be visible. However, from the
maximum frequencies illustrated (50pulses/sec for soleus and 125 pulses/
secforF.H.L.) anyfurtherincreaseinfrequencyproducesnegligible change
inthepeaktensiondevelopedbythemuscle. Definitionmustherebemade
of peak tension since, while the fast muscles usually show a plateau of
tension, the slow muscles often show a slow rise of tension for several
hundred milliseconds after the initial faster rise. Peak tension will there-
fore be defined for the purposes of this paper as the maximum tension
reached 400msec after the first stimulus ofa tetanic train, since by this
time any residual climb in tension is small.
While it is true that no increase occurs in the peak tension developed if
the stimulation frequency exceeds 50pulses/sec for soleus and 125pulses/
sec for F.H.L. it is apparent from Fig. 3 that the rate at which the peak
tension is developed is considerably enhanced by further increases in the
stimulation frequency. Figure 3 shows superimposed isometric tension
records of two tetani of soleus at stimulation rates of 50 pulses/sec and
310 pulses/sec and two tetani ofF.H.L. at stimulation rates of 125 pulses/
sec and 500pulses/sec.
In order to study this change in the rate oftension development more
closely differentiated records of the tension rise were employed (see
Methods) andanillustrationofsuchrecordsobtainedduringtetanicstimu-
lation are showninthe lower beam recordings ofFig. 4. The differentiated
tension records serve in fact to increase the effective amplification ofthe
recording system and clearly demonstrate changes in the rate of tension
build up with time. In the lower oscillographic records ofboth the soleus
tetanusat50pulses/secandtheflexorhallucislongustetanusat 125 pulses/
sec obvious oscillations are apparent while with the tetani at 310pulses/
sec and 500 pulses/sec the differentiated records are much smoother.
Close examination ofFig. 4 will also show that in both the slow and fast
musclethemaximumrate ofchange oftension (thepeakofthe differential
record) is greater and occurs earlier with the higher frequency ofstimula-
tion. This latter point is illustratedin Fig. 5A,where the maximumrateof
changeoftensionmeasureding/msecisplottedagainststimulusfrequency.
The filled circles show the maximum rate ofrise oftension during a single
twitch, the crosses show points observed with increasing stimulus fre-
quency and the open circles points obtained with decreasing stimulus
frequency. For any particular muscle the shape ofthe curve is extremely
reproducible from animal to animal, though the absolute value in g/msec
varies.
In order to compare the maximum rate oftension development during
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
ISOMETRIC TETANI OF MAMMALIAN MUSCLES 343
isometric tetani in different animals use was made ofa derived term-the
percentage ofthe maximum tetanic tension (defined above) developedper
msec (%P0/msec). ItmaybeseenfromFig. 5Bthatslow andfastmuscles
Soleus F.H.L.
500g
................................ I kg . ...........
10msec 1-5kg 10msec
Fig. 3. Left. Superimposedtetani ofsoleus muscle at stimulationfrequencies of
50 pulses/sec (lower record) and 310 pulses/sec (upper record). Right. Similar
records (at different sweep speed) for F.H.L. at stimulation frequencies of
125 pulses/sec (lower record) and 500 pulses/sec (upper record). Tension calibra-
tionsof500g, 1 and 1-5kg.
-Soleus F.H.L.
50 125
_
500g
1 kg
1-5kg
310 500
.......................................... ......... .. . . . . . . . . . . ..
10msec 10msec
Fig. 4. Paired recordings of isometric tension development and differentiated
tensionrecordsforsoleus(left)andF.H.L.muscle(right).Thestimulationfrequencies
used are shown under each pair ofrecords. Note the different sweep speeds for
soleusand F.H.L. Differenttimeconstantsofdifferentiationwereusedforthetwo
muscles.
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008
344 A. J. BULLER AND D. M. LEWIS
typified by soleus and F.H.L. have clearly distinct maximum rates ofrise,
and that by plotting the time to peak tension of the isometric twitch
response against the maximum rate of tension development in isometric
tetani two distinct populations of points occur, filled circles representing
F.H.L. muscles and crosses soleus muscles.
25 A
Soleus -3
I ~~~~0x
15 - Ox x Ox 2
E -e
-1 5
30 t -2
10
10~) 20 50 100 200 20
Stimulation frequency (pulses/see) Timeto peak (msec)
Fig. 5A. Plot of the maxrimum rate of tension development (ordinate) during
tetaniofthefrequencyshown (abscissa) forsoleusanldF.H.L. Thetwofilledcircles
indicate the maxrimum rate oftension development during a twitch. The crosses
indicate the maximum rates measured during a series oftetani ofincreasing fre-
quency, the open circles the maximulm rates observed with a series oftetani of
decreasing frequency. The durations of the tetani were 200 msec for soleus and
100msecforF.H.L.Thetwoshortarrowsindicatethefrequenciescommonlyquoted
inthe literatureasthe'fusionfrequencies'for slowand fastmuscles,respectively.
The longer arrows indicate the absolute refractory periods between the first and
secondstimuliinthetwomusclesusedinthisexrperiment. Theordinatescalestothe
right ofthe two graphs indicatethemaxrimum rate oftensiondevelopment inthe
twomusclesatvariousfrequenciesofstimulationwiththemaximumrateobserved
inthe twitchscaled as one.
Fig. 5B. A plot ofthe time from the start ofcontraction tothe development of
peaktensioninanisometrictwitch(abscissa)againstthemaximumrateoftension
developmentduringanisometrictetanus(ordinate). Crossesindicatesoleusmuscles,
filled circles F.H.L. muscles.
We were initially surprised at the high frequency of stimulation
necessary to produce the maxsimulm rate of rise of tension in both soleus
and flexor hallucis longus. While it may easily be shown that the large
diametermotor axonLs supplying bothsoleus andF.H.L. muscle can conduct
trains ofimpulses at such repetition rates, it was decided to make a direct
attempttorecordthemuscleelectricalactivityinorderto confirm thatthe
muscleactionpotentialswerefollowing thestimulation frequency. Bipolar
Downloaded from jp.physoc.org at BIUSJ (Paris 6) on March 5, 2008