Peeled mammalian skeletal muscle fibers. Possible stimulation of Ca2+ release via a transverse tubule-sarcoplasmic reticulum mechanism.
Single muscle fibers from rabbit soleus and adductor magnus and from semitendinosus muscles were peeled to remove the sarcolemma and then stimulated to release Ca2+ by (a) caffeine application or (b) ionic depolarization accomplished via substitution of choline chloride for potassium propionate at constant [K+] X [Cl-] in the bathing solution. Each stimulus, ionic or caffeine, elicited an isometric tension transient that appeared to be due to Ca2+ released from the sarcoplasmic reticulum (SR). The peak magnitude of the ionic (Cl- -induced) tension transient increased with increasing Cl- concentration. The application of ouabain to fibers after peeling had no effect on either type of tension transient. However, soaking the fibers in a ouabain solution before peeling blocked the Cl- -induced but not the caffeine-induced tension transient, which suggests that ouabain's site of action is extracellular, perhaps inside transverse tubules (TTs). Treating the peeled fibers with saponin, which should disrupt TTs to a greater extent than SR membrane, greatly reduced or eliminated the Cl- -induced tension transient without significantly altering the caffeine-induced tension transient. These results suggest that the Cl- -induced tension transient is elicited via stimulation of sealed, polarized TTs rather than via ionic depolarization of the SR.
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011817:Rabbits; D012503:Saponins / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
D002712:Chlorides; D012503:Saponins; D002110:Caffeine; D010042:Ouabain; D002118:Calcium