A fast-twitch oxidative-glycolytic muscle with a robust inward calcium current.
This report describes the histochemical and physiological properties of a rat skeletal muscle with a robust activity-dependent slow inward Ca2+ current. The muscle, the flexor digitorum brevis (FDB), is a small plantar flexor from the hindfoot. It is a homogeneous muscle consisting of approximately 90% fast-twitch oxidative-glycolytic (type IIA) fibers. Stimulation of the FDB with repetitive stimulus trains (30 or 50 Hz for 330 ms, 1 train/s for 2-5 min) produced a slow increase in the base-line or resting tension of the muscle between trains. This progressive increase in resting tension appears to be due to the activation of voltage-dependent slow Ca2+ channels, since it could be eliminated (i) by stimulating the muscle in a medium containing 2 mM EGTA and without Ca2+, and (ii) by the addition of either Co2+ or verapamil. The presence of a slow current may be associated with an increase in K+ efflux as stimulation continues, and with a prolongation of relaxation time. We also propose that the slow Ca2+ current may contribute to the allosteric activation of phosphorylase kinase during muscle activity. The FDB provides an excellent preparation to investigate the regulation of muscle metabolism by intra- and extra-cellular Ca2+ during exercise.
R C
RC
Carlsen
D B
DB
Larson
D A
DA
Walsh
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004558:Electric Stimulation; D005221:Fatigue; D005260:Female; D006019:Glycolysis; D006145:Guanethidine / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
D007473:Ion Channels; D004533:Egtazic Acid; D014700:Verapamil; D002118:Calcium; D006145:Guanethidine