EFFECT OF PURINERGIC BLOCKERS ON OUTWARD CURRENT IN ISOLATED SMOOTH-MUSCLE CELLS OF THE SHEEP BLADDER

Freshly dispersed cells from sheep urinary bladder were voltage clampe d using the whole cell and inside-out patch-clamp technique. Cibacron and Basilen blue increased outward current in a dose-dependent manner with a half-maximal response at 10(-5) M. Suramin, in concentrations t o 10(-3) M, had no such effect. The Cibacron blue response was abolish ed in Ca2+-free physiological salt solution, suggesting that it was ac ting on a Ca2+-dependent current. Similarly, the Cibacron blue-sensiti ve current was significantly attenuated by charybdotoxin. Cibacron blu e did not modulate inward current nor were its effects modified by caf feine or heparin, suggesting that its effect on outward current was no t secondary to an increase in intracellular Ca2+. Application of 10(-4 ) M Cibacron blue to the inside membrane of excised patches caused a r apid increase in open probability of a large-conductance (300 pS) K+ c hannel. These results suggest that Cibacron blue is a potent activator of a Ca2+-dependent outward current in bladder smooth muscle cells in addition to its action as a purinergic blocker.