期刊
CANADIAN JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY
卷 83, 期 10, 页码 857-864出版社
CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/Y05-090
关键词
chemo-mechanical transduction; activation-contraction coupling; cross-bridge; myosin light chain kinase; myosin light chain phosphatase; phosphorylation; cooperativity
资金
- NHLBI NIH HHS [R01 HL071191-03, R01 HL071191, HL71191] Funding Source: Medline
- NIDDK NIH HHS [DK56034, R01 DK056034] Funding Source: Medline
In contrast to striated muscle, both normalized force and shortening velocities are regulated functions of cross-bridge phosphorylation in smooth muscle. Physiologically this is manifested as relatively fast rates of contraction associated with transiently high levels of cross-bridge phosphorylation. In sustained contractions, Ca2+, cross-bridge phosphorylation, and ATP consumption rates fall, a phenomenon termed latch. This review focuses on the Hai and Murphy (1988a) model that predicted the highly non-linear dependence of force on phosphorylation and a directly proportional dependence of shortening velocity on phosphorylation. This model hypothesized that (i) cross-bridge phosphorylation was obligatory for cross-bridge attachment, but also that (ii) dephosphorylation of an attached cross-bridge reduced its detachment rate. The resulting variety of cross-bridge cycles as predicted by the model could explain the observed dependencies of force and velocity on cross-bridge phosphorylation. New evidence supports modifications for more general applicability. First, myosin light chain phosphatase activity is regulated. Activation of myosin phosphatase is best demonstrated with inhibitory regulatory mechanisms acting via nitric oxide. The second modification of the model incorporates cooperativity in cross-bridge attachment to predict improved data on the dependence of force on phosphorylation. The molecular basis for cooperativity is unknown, but may involve thin filament proteins absent in striated muscle.
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