Source of calcium for contractions induced by depolarization and muscarinic receptor stimulation in rabbit urinary bladder

Source of calcium for contractions induced by depolarization and muscarinic receptor stimulation in rabbit urinary bladder. Acta Physiol Scand 130 , 545–551. Received 4 December 1986, accepted 20 March 1987. ISSN 0001–6772. Departments of Obstetrics and Gynaecology and Clinical Pharmacology, University of Lund, and AB Leo Research Laboratories, Helsingborg, Sweden. Omission of calcium or the inclusion of lanthanum in the bathing medium resulted in an almost complete inhibition of contractile responses induced by either K + depolarization or carbachol in strips of rabbit urinary bladder. D‐600 inhibited K + ‐induced contractions significantly more than carbachol‐induced responses. The influx of 45 Ca into cells was stimulated both by K + depolarization and carbachol. Over a 2‐min period the increase in 46 Ca influx induced by high K + and carbachol was 98 and 65%, respectively. Both lanthanum and D‐600 blocked 45 Ca influx stimulated by either K + depolarization or carbachol. The inhibition of 45 Ca influx by these calcium‐channel blocking agents, particularly by D‐600, was dependent on the length of exposure. Application of carbachol during 45 Ca efflux in pre‐loaded muscle strips had no effect on the rate of 45 Ca efflux. These results indicate that the contractile responses of the urinary bladder to depolarization and to carbachol are highly dependent on an extracellular source of calcium.