Effect of extracellular calcium and calcium‐blocking agents on detrusor contractility: An in vitro study

The effects of varying concentrations of calcium in the bathing solution and the effects of varying doses of the calcium‐blocking agents verapamil, diltiazem, and nifedipine on baseline tension, magnitude, and frequency of spontaneous contractions and on the contractile responses to acetylcholine, bethanechol, and electrical stimulation were tested on guinea pig bladder muscle strips suspended in a muscle bath. Over a wide range of calcium concentration (10 −6 −4.8 × 10 −3 M) no significant changes were noted in the aforementioned spontaneous and induced contractile activity. All parameters were, however, significantly depressed in a calcium‐free bathing solution. At doses of 1.0 and 2.0 μg/ml bath each of the calcium‐blocking agents significantly depressed the aforementioned spontaneous and induced smooth muscle contractile activity.