In vitro dog detrusor strip contractile responses and calcium ion activity

In vitro detrusor strip experiments show that the presence of calcium ion is essential for spontaneous and bethanechol-induced detrusor contractile activity. 45Ca uptake experiments show that detrusor strips subjected to bethanechol show increased 45Ca uptake with significant decrease in total muscle strip calcium. There is a significant increase in the percentage of calcium exchange, suggesting that calcium efflux has exceeded influx. Kinetic analysis of 45Ca uptake by detrusor strips shows more 45Ca to reside in the slow component of strips following exposure to bethanechol. This suggests that calcium associated with bethanechol-induced contractile activity comes to occupy intracellular or more tightly bound membrane sites.