Inhibition by papaverine of calcium movements and tension in the smooth muscles of rat vas deferens and urinary bladder.

Papaverine, up to 150 micron, was without effect on resting tension of vas deferens and urinary bladder smooth muscle strips, but caused a dose-dependent inhibition of the phasic component of the 100 mM-K contracture. At 150 micron, papaverine caused an 80 and 60% inhibition of phasic tension in vas deferens and urinary bladder muscle respectively. Papaverine caused a marked dose-dependent reduction in the tonic component of 100 mM-K contractures in both preparations. At 150 micron, papaverine often relaxed preparations below initial starting tension. Addition of 150 micron-papaverine to incubation media caused a fall of 25-30% in 45Ca uptake by both preparations. Papaverine at 150 micron caused a small fall in resting 45Ca efflux from vas deferens and a larger fall in efflux from bladder muscle. However, this papaverine concentration caused a large inhibition of the 45Ca uptake by and 45Ca efflux from both preparations when stimulated by high-K depolarization. Papaverine at 150 micron was without significant effect on Ca binding by either microsomes or mitochondria isolated from both vas deferens and urinary bladder smooth muscle. The main site of papaverine action appears to be on the Ca-influx mechanism responsible for regulating Ca entry during prolonged K depolarization.

Papaverine-induced inhibition of electrical and mechanical activity and calcium movements of rat ileal smooth muscle.

1. Papaverine, in the concentration range 50-150 microM, inhibited rhythmic spontaneous contraction and caused relaxation of KCl-induced contractures of rat ileal smooth muscle. 2. Spontaneous slow waves and spikes declined at low papaverine concentrations. 3. The normal 45Ca uptake of the ileum was reduced by papaverin. Although papaverine caused only a small inhibition of normal 45Ca efflux from the ileum, it strongly inhibited the KCl-induced stimulation of 45Ca efflux. 4. Calcium uptake by the isolated ileal smooth-muscle microsomal fraction was slightly increased by papaverine, but mitochondrial calcium uptake was unaffected. 5. Ileal smooth muscle incubated in calcium-free media showed little response to either the reintroduction of calcium or KCl in the presence of papaverine. 6. It is suggested that the inhibitory actions of papaverine on ileal smooth muscle result from a blockade of the calcium influx which triggers the excitation-contraction coupling sequence.