title: Length-dependent effects of osmotic compression on skinned rabbit psoas muscle fibers.
abstract: The goal of this study was to characterize the interrelationship between sarcomere length and interfilament spacing in the control of Ca2+ sensitivity in skinned rabbit psoas muscle fibers. Measurements were made at sarcomere lengths 2.0, 2.7 and 3.4 microm. At 2.7 microm the fiber width was reduced by 17% relative to that at 2.0 microm and the pCa50 for force development was increased by approximately 0.3 pCa units. In the presence of 5% Dextran T-500 the fiber width at sarcomere length 2.0 microm was also decreased by 17% and the Ca2+ sensitivity was increased to the same value as at 2.7 microm. In contrast, at sarcomere length 2.7 microm the addition of as much as 10% Dextran T-500 had no effect on Ca2+ sensitivity. At sarcomere length 3.4 microm there was an additional 7% compression and the Ca2+ sensitivity was increased slightly (approximately 0.1 pCa units) relative to that at 2.7 microm. However at 3.4 microm the addition of 5% Dextran T-500 caused the Ca2+ sensitivity to decrease to the level seen at 2.0 microm. Given that the skinning process causes a swelling of the filament lattice it is evident that the relationship between sarcomere length and Ca2+ sensitivity observed in skinned fibers may not always be applicable to intact fibers. These data are consistent with measurements of Ca2+ in intact fibers which indicate that there might be a decline in Ca2+ sensitivity at long sarcomere lengths.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsbhugh School of Medicine, PA 15261, USA.
authors.forename: Y P
authors.initials: YP
authors.lastname: Wang
authors.forename: F
authors.initials: F
authors.lastname: Fuchs
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003911:Dextrans / Q000494:pharmacology; D009997:Osmotic Pressure; D016658:Psoas Muscles / Q000033:anatomy & histology* / Q000502:physiology*; D011817:Rabbits; D012518:Sarcomeres / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
chemical_list: D003911:Dextrans; D002118:Calcium