Kinetics of Ca2+ release and contraction induced by photolysis of caged D-myo-inositol 1,4,5-trisphosphate in smooth muscle. The effects of heparin, procaine, and adenine nucleotides.
The kinetics of Ca2+ release and contraction induced by photolytic release of inositol 1,4,5-trisphosphate (InsP3) were determined in permeabilized smooth muscle. The rate of Ca2+ release was half-maximal at 1 microM InsP3. The concentration-dependent delay of Ca2+ release at saturating InsP3 concentration was approximately 10 ms and within the uncertainty of the measurements. The relationship between the delay and InsP3 concentration showed no evidence of a high level (n = 4 or higher) of cooperativity but could not distinguish between no cooperativity (n = 1) or a low level (n = 2) of cooperativity. Submaximal [InsP3] caused only partial Ca2+ release from the InsP3-sensitive stores. InsP3-induced Ca2+ release was markedly potentiated by ATP or by adenosine 5'-(beta,gamma-methylene-triphosphate), but neither the rate nor the amplitude of release was significantly affected by procaine (2-5 mM). Heparin increased the delay between photolysis and Ca2+ release, indicating that the off rate of inert ligand(s) bound to InsP3 receptors may contribute to the physiological delay in Ca2+ release. There was a much longer (370 ms +/- 45 S.E.) delay between the rise of Ca2+ and force development, presumably reflecting events preceding and associated with myosin light chain phosphorylation.
Somlyo
A V
AV
Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908.
Horiuti
K
K
Trentham
D R
DR
Kitazawa
T
T
Somlyo
A P
AP
D000227:Adenine Nucleotides / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006168:Guinea Pigs; D006493:Heparin / Q000494:pharmacology*; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011343:Procaine / Q000494:pharmacology*; D013997:Time Factors
D000227:Adenine Nucleotides; D011343:Procaine; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium