Comparison of calcium release from sarcoplasmic reticulum of slow and fast twitch muscles.
The mechanism of Ca2+ release from the sarcoplasmic reticulum (SR) of slow and fast twitch muscle was compared by examining biochemical characteristics, ryanodine binding, Ca2+ efflux, and single Ca2+ channel properties of SR vesicles. Although many features of the Ca2+ release channel were comparable, two functional assays revealed remarkable differences. The comparable properties include: a high molecular weight protein from both types of muscle was immunologically equivalent, and Scatchard analysis of [3H]ryanodine binding to SR showed that the Kd was similar for slow and fast SR. In the flux assay the sensitivity to the agonists caffeine, doxorubicin, and Ca2+ and the antagonists Mg2+, ruthenium red, and tetracaine differed only slightly. When SR vesicles were incorporated into lipid bilayers, the single-channel conductances of the Ca2+ release channels were indistinguishable. The distinguishing properties are: When Ca2+ release from passively 45Ca(2+)-loaded SR were monitored by rapid filtration, the initial rates of Ca2+ release induced by Ca2+ and caffeine were three times lower in slow SR than in fast SR. Similarly, when Ca2+ release channels were incorporated into lipid bilayers, the open probability of the slow SR channel was markedly less, mainly due to a longer mean closed time. Our results indicate that slow and fast muscle have ryanodine receptors that are biochemically analogous, yet functional differences in the Ca2+ release channel may contribute to the different time to peak contraction observed in intact slow and fast muscles.
Lee
Y S
YS
Department of Medicine, University of Connecticut Health Center, Farmington 06030.
Ondrias
K
K
Duhl
A J
AJ
Ehrlich
B E
BE
Kim
D H
DH
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D004317:Doxorubicin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D013748:Tetracaine / Q000494:pharmacology
D015220:Calcium Channels; D013748:Tetracaine; D012430:Ruthenium Red; D012433:Ryanodine; D002110:Caffeine; D004317:Doxorubicin; D008274:Magnesium; D002118:Calcium