Effects of Vasodilator Agents on Smooth Muscle Cells of the Coronary Artery of the Pig

1 Effects of the vasodilator agents, papaverine, diltiazem, and sodium nitroprusside (SNP) on the electrical and mechanical activities of the smooth muscles of the coronary artery of the pig were compared.2 At a concentration of 10(-5) M, papaverine hyperpolarized and increased the ionic conductance of the membrane, SNP slightly hyperpolarized but diltiazem had no effect on the membrane potential and membrane ionic conductance.3 At a concentration of 10(-5) M, diltiazem abolished the spike evoked by outward current pulses in the presence of tetraethylammonium (TEA) 10 mM, while papaverine and SNP slightly reduced spike amplitude.4 The K-induced contraction produced by any given concentration of [K](o) over 20.2 mM was suppressed by diltiazem and SNP dose-dependently in concentrations greater than 10(-6) M; higher concentrations of papaverine were required to suppress contraction.5 The acetylcholine (ACh)-induced contraction was suppressed by diltiazem and SNP at concentrations greater than 10(-6) M and by papaverine in concentrations over 10(-5) M.6 In saponin-treated skinned muscles, papaverine, diltiazem and SNP had no effect on the pCa-tension relationship, i.e. these agents had no effect on the Ca receptor of contractile proteins. Furthermore, the caffeine-induced contraction in skinned muscles (after Ca loading) was not affected by these agents, i.e. the mechanism of Ca release by caffeine in skinned muscles was not affected.7 Chlorpromazine, an agent interacting with calmodulin, antagonized the contractile effect of calcium on skinned muscle fibres.8 The results obtained are discussed in relation to spike and contraction generating mechanisms, i.e. the effects of these agents on Ca influx and Ca release from stored sites. The results indicated that at equimolar concentrations diltiazem suppressed the mechanical response in the coronary artery of the pig more than SNP or papaverine.