Role of calcium ion antagonists of the bladder detrusor muscle: in vitro and in vivo study.
Calcium (Ca2+) ions play an important role in the contractility of the detrusor. Most of the neurotransmitters and modulators act on the detrusor through altering the final intracellular concentration of Ca2+. We studied three commonly used Ca2+ antagonists on their effect of detrusor contractility in vitro: verapamil, nifedipine and segontin. All three inhibited the detrusor-induced contraction in a dose-dependent fashion. Verapamil showed noncompetitive inhibition. Segontin showed a competitive inhibition on both phasic and tonic contractions of the detrusor strips. Nifedipine selectively inhibited the phasic contraction noncompetitively but competitively suppressed the tonic contraction. The in vivo application of verapamil on the bladder of rabbits with multiple-sclerosis-like disease showed a significant increase in bladder capacity. The study shows the possibility of the potential use of Ca2+-antagonist to suppress the problem of bladder instability.