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Substrate and product dependence of force and shortening in fast and slow smooth muscle

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Author

Summary, in English

To explore the molecular mechanisms responsible for the variation in smooth muscle contractile kinetics, the influence of MgATP, MgADP, and inorganic phosphate (P(i)) on force and shortening velocity in thiophosphorylated "fast" (taenia coli: maximal shortening velocity Vmax = 0.11 ML/s) and "slow" (aorta: Vmax = 0.015 ML/s) smooth muscle from the guinea pig were compared. P(i) inhibited active force with minor effects on the V(max). In the taenia coli, 20 mM P(i) inhibited force by 25%. In the aorta, the effect was markedly less (< 10%), suggesting differences between fast and slow smooth muscles in the binding of P(i) or in the relative population of P(i) binding states during cycling. Lowering of MgATP reduced force and V(max). The aorta was less sensitive to reduction in MgATP (Km for Vmax: 80 microM) than the taenia coli (Km for Vmax: 350 microM). Thus, velocity is controlled by steps preceding the ATP binding and cross-bridge dissociation, and a weaker binding of ATP is not responsible for the lower V(max) in the slow muscle. MgADP inhibited force and V(max). Saturating concentrations of ADP did not completely inhibit maximal shortening velocity. The effect of ADP on Vmax was observed at lower concentrations in the aorta compared with the taenia coli, suggesting that the ADP binding to phosphorylated and cycling cross-bridges is stronger in slow compared with fast smooth muscle.

Publishing year

2001

Language

English

Pages

407-418

Publication/Series

Journal of General Physiology

Volume

117

Issue

5

Document type

Journal article

Publisher

Rockefeller Institute for Medical Research

Topic

  • Pharmacology and Toxicology
  • Physiology
  • Medicinal Chemistry

Keywords

  • ADP
  • ATP
  • phosphate
  • myosin isoforms
  • force-velocity relation

Status

Published

Research group

  • Vascular Physiology

ISBN/ISSN/Other

  • ISSN: 0022-1295