The role of Ca-activated Cl current in tone generation in the rabbit corpus cavernosum.

Rabbit corpus cavernosum smooth muscle (RCCSM) cells express ion channels that produce Ca-activated Cl () current, but low sensitivity to conventional antagonists has made its role in tone generation difficult to evaluate. We have reexamined this question using two new generation blockers, T16A-A01 and CaCC-A01. Isolated RCCSM cells were studied using the perforated patch method. Current-voltage protocols revealed that both L-type Ca current and T16A-A01 and CaCC-A01 (10 μM) reduced by ~85%, while 30 μM abolished it. L-type Ca current was unaffected by 10 μM CaCC-A01 but was reduced by 50% at 30 μM CaCC-A01, 46% at 10 μM T16A-A01, and 78% at 30 μM T16A-A01. Both drugs reduced spontaneous isometric tension in RCCSM strips, by 60-70% at 10 μM and >90% at 30 μM. Phenylephrine (PE)-enhanced tension was also reduced (ED = 3 μM, CaCC-A01; 14 μM, T16A-A01). CaCC-A01 at 10 μM had little effect on 60 mM KCl contractures, though they were reduced by 30 μM CaCC-A01 and T16A-A01 (10 μM and 30 μM) consistent with their effects on L-type Ca current. Both drugs also reversed the stimulatory effect of PE on intracellular Ca waves, studied with laser scanning confocal microscopy in isolated RCCSM cells. In conclusion, although both drugs were effective blockers of , the effect of T16A-A01 on L-type Ca current precludes its use for evaluating the role of in tone generation. However, 10 μM CaCC-A01 selectively blocked versus L-type Ca current and reduced spontaneous and PE-induced tone, suggesting that is important in maintaining penile detumescence.