AJP - Cell Physiology, Vol 270, Issue 3 C969-C973, Copyright © 1996 by American Physiological Society
Effect of purinergic blockers on outward current in isolated smooth muscle cells of the sheep bladder
K. D. Cotton, M. A. Hollywood, K. D. Thornbury and N. G. McHale
School of Biomedical Science, The Queen's University of Belfast, Northern Ireland, United Kingdom.
Freshly dispersed cells from sheep urinary bladder were voltage clamped
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 to 10(-3)M,
had no such effect. The Cibacron blue response was abolished in Ca2+ -free
physiological salt solution, suggesting that it was acting on a Ca2+
-dependent current. Similarly, the Cibacron blue-sensitive current was
significantly attenuated by charybdotoxin. Cibacron blue did not modulate
inward current nor were its effects modified by caffeine or heparin,
suggesting that its effect on outward current was not secondary to an
increase in intracellular Ca2+. Application of 10(-4)M Cibacron blue to the
inside membrane of excised patches caused a rapid increase in open
probability of a large conductance (300 pS) K+ channel. 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.
