Effect of phorbol esters on cytosolic Ca2+ level, myosin phosphorylation and muscle tension in high K(+)-stimulated bovine tracheal smooth muscle.
To determine the role of protein kinase C (PKC) in bovine tracheal smooth muscle contractility, we examined the effects of phorbol esters on cytosolic Ca2+ level ([Ca2+]i), myosin light chain (MLC) phosphorylation and contractile force in intact muscle and contraction in a permeabilized preparation. In intact muscle, 12-deoxyphorbol 13-isobutyrate (DPB, 1 microM) increased the force without changing [Ca2+]i. High K+ (72.7 mM) induced sustained contraction with sustained increase in [Ca2+]i. In the muscle stimulated by high K+, 50 nM DPB increased the contractile force without changing [Ca2+]i, and 1 microM DPB increased the contractile force with decreasing [Ca2+]i. Thus DPB shifted the [Ca2+]i/force relationship for high K+ to the lower [Ca2+]i in a concentration-dependent manner. In permeabilized muscle, DPB did not induce contraction in the absence of Ca2+ (< < 0 nM), but shifted the Ca2+/force relationship to the lower Ca2+ levels. In the muscle stimulated with high K+, DPB (50 nM and 1 microM) increased MLC phosphorylation and force without changing the MLC phosphorylation/force relationship. DPB (1 microM) increased PKC activity estimated by the translocation from the cytoplasm to the membrane. These results suggest that DPB increases the Ca2+ sensitivity of MLC phosphorylation via the activation of PKC. Furthermore, DPB at higher concentration has an inhibitory effect on stimulated [Ca2+]i.
Tajimi
M
M
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, University of Tokyo, Japan.
Hori
M
M
Ozaki
H
H
Karaki
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D014132:Trachea / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D018994:Myosin Light Chains; D010703:Phorbol Esters; D014700:Verapamil; D011493:Protein Kinase C; D009218:Myosins; D002118:Calcium