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




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*