HETERO

Heterogeneity of muscle tissues

This summary table was designed as a revision aid. It has been simplified to fit onto one page, and is not intended to be a definitive account. Note in particular that smooth muscles are a very heterogeneous group, and that individual exceptions can be found to the generalisations in the rightmost column. These data apply to healthy individuals.

feature voluntary skeletal muscle fibre types cardiac
muscle
smooth
muscles

type 2B type 2A type 1

colour white red red red variable

appearance striated striated striated striated no striations

shortening 20% 20% 20% 20% 50%

dystrophin yes yes yes yes utrophin

titin yes yes yes yes no

nebulin yes yes yes nebulette no

actin : myosin 7 : 1 7 : 1 7 : 1 7 : 1 15 : 1

myosin ATPase high high low lower very low

contract speed fast fast slow slower very slow

myosin lc kinase minor role minor role minor role minor role important

actin regulation troponin troponin troponin troponin caldesmon

duty cycle occasional intermittent sustained continuous continuous

fatigue very rapid rare very rare none none

main fuel glucose versatile fats, ketones fats, ketones ?

blood supply poor good adequate excellent adequate

cell shape long & fat long & thin long & thin small small

cell nuclei thousands thousands thousands one one

resting potential 80mV 80mV 80mV 80mV 30-50mV

excitation all or none all or none all or none all or none variable

active tension fixed fixed fixed variable variable

action potential spike spike spike plateau variable

gap junctions none none none every cell common

external calcium no effect no effect no effect essential essential

verapamil no effect no effect no effect -ve inotrope relaxes

phospholamban no no no yes no

Na/Ca antiport no no no yes no

AcCh receptors nicotinic nicotinic nicotinic muscarinic muscarinic

AcCh effect contracts contracts contracts -ve inotrope contracts

alpha adrenergic no no no no some types

alpha effect none none none none contraction

beta adrenergic yes yes yes yes some types

beta effect metabolic metabolic metabolic +ve inotrope relaxation

other agonists
(* present only in a few cell types)
cortisol insulin cortisol insulin cortisol insulin cortisol insulin cortisol insulin angiotensin* serotonin* oxytocin* VIP* and numerous other gut peptides*

feature	voluntary skeletal muscle fibre types			cardiac muscle	smooth muscles
feature	type 2B	type 2A	type 1	cardiac muscle	smooth muscles
colour	white	red	red	red	variable
appearance	striated	striated	striated	striated	no striations
shortening	20%	20%	20%	20%	50%
dystrophin	yes	yes	yes	yes	utrophin
titin	yes	yes	yes	yes	no
nebulin	yes	yes	yes	nebulette	no
actin : myosin	7 : 1	7 : 1	7 : 1	7 : 1	15 : 1
myosin ATPase	high	high	low	lower	very low
contract speed	fast	fast	slow	slower	very slow
myosin lc kinase	minor role	minor role	minor role	minor role	important
actin regulation	troponin	troponin	troponin	troponin	caldesmon
duty cycle	occasional	intermittent	sustained	continuous	continuous
fatigue	very rapid	rare	very rare	none	none
main fuel	glucose	versatile	fats, ketones	fats, ketones	?
blood supply	poor	good	adequate	excellent	adequate
cell shape	long & fat	long & thin	long & thin	small	small
cell nuclei	thousands	thousands	thousands	one	one
resting potential	80mV	80mV	80mV	80mV	30-50mV
excitation	all or none	all or none	all or none	all or none	variable
active tension	fixed	fixed	fixed	variable	variable
action potential	spike	spike	spike	plateau	variable
gap junctions	none	none	none	every cell	common
external calcium	no effect	no effect	no effect	essential	essential
verapamil	no effect	no effect	no effect	-ve inotrope	relaxes
phospholamban	no	no	no	yes	no
Na/Ca antiport	no	no	no	yes	no
AcCh receptors	nicotinic	nicotinic	nicotinic	muscarinic	muscarinic
AcCh effect	contracts	contracts	contracts	-ve inotrope	contracts
alpha adrenergic	no	no	no	no	some types
alpha effect	none	none	none	none	contraction
beta adrenergic	yes	yes	yes	yes	some types
beta effect	metabolic	metabolic	metabolic	+ve inotrope	relaxation
other agonists (* present only in a few cell types)	cortisol insulin	cortisol insulin	cortisol insulin	cortisol insulin	cortisol insulin angiotensin* serotonin* oxytocin* VIP* and numerous other gut peptides*