The role of Ca2+-activated Cl− current in tone generation in the rabbit corpus cavernosum

Rabbit corpus cavernosum smooth muscle (RCCSM) cells express ion channels that produce Ca 2+ -activated Cl - ( I ClCa ) 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 I ClCa blockers, T16A inh -A01 and CaCC inh -A01. Isolated RCCSM cells were studied using the perforated patch method. Current-voltage protocols revealed that both L-type Ca 2+ current and I ClCa T16A inh -A01 and CaCC inh -A01 (10 μM) reduced I ClCa by ~85%, while 30 μM abolished it. L-type Ca 2+ current was unaffected by 10 μM CaCC inh -A01 but was reduced by 50% at 30 μM CaCC inh -A01, 46% at 10 μM T16A inh -A01, and 78% at 30 μM T16A inh -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 50  = 3 μM, CaCC inh -A01; 14 μM, T16A inh -A01). CaCC inh -A01 at 10 μM had little effect on 60 mM KCl contractures, though they were reduced by 30 μM CaCC inh -A01 and T16A inh -A01 (10 μM and 30 μM) consistent with their effects on L-type Ca 2+ current. Both drugs also reversed the stimulatory effect of PE on intracellular Ca 2+ waves, studied with laser scanning confocal microscopy in isolated RCCSM cells. In conclusion, although both drugs were effective blockers of I ClCa , the effect of T16A inh -A01 on L-type Ca 2+ current precludes its use for evaluating the role of I ClCa in tone generation. However, 10 μM CaCC inh -A01 selectively blocked I ClCa versus L-type Ca 2+ current and reduced spontaneous and PE-induced tone, suggesting tha I ClCa is important in maintaining penile detumescence.