title: Influence of osmotic compression on calcium activation and tension in skinned muscle fibers of the rabbit.
abstract: Single skinned muscle fibers were osmotically compressed back to and below their in situ size by addition of a large, random-coil polymer (Deytran T500; MN = 180,000; MW = 461,000) to the bathing medium. Maximal Ca2+-activated tension in fibers swollen (zero Dextran, fiber width 21% above in situ) or near in situ size (5% Dextran, in g/100 ml final solution) was similar, but compression to 86% of in situ width with 10% Dextran decreased maximal force by 15% relative to polymer-free control. While the relative tension-pCa relation in 0 and 10% Dextran was similar, with a pCa of 6.37 required for 50% activation, that in 5% Dextran was more sensitive to Ca2+, with a pCa50 of 6.66. We feel these effects are most likely due to changes in interfilament spacing with compression and that alterations in Ca2+-sensitivity might be explained by changes in cross-bridge angle or in the concomitant attachment-detachment rate constants which would be expected to influence the troponin-Ca2+ binding equilibrium, as has been proposed by others.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009997:Osmotic Pressure; D011817:Rabbits
chemical_list: D002118:Calcium