Possible underestimation of the channel conductance underlying pinacidil-induced K+ currents using noise analysis in pig urethral myocytes

Electrophysiological and pharmacological properties of the pinacidil-induce d K+ currents in isolated cells from pig urethra were investigated using pa tch-clamp techniques. Pinacidil (100 muM) induced an outward current at -50mV which gradually dec reased. Under current-clamp conditions, 100 muM pinacidil induced a hyperpo larization that was sustained. This suggests that activation of only a few channels can hyperpolarize the membrane. At a holding potential of -50mV, g libenclamide inhibited the pinacidil-induced current with a single exponent ial time course. Unitary current recordings in symmetrical 140 mM K+ conditions demonstrated that pinacidil activates a 43-pS, glibenclamide-sensitive K+ channel (i.e. K-ATP channel). Analysis of the basal noise of the pinacidil-induced macro scopic currents from -90 mV to -30 mV yielded estimates of channel conducta nce (6pS) which were much smaller, and probably an underestimate. These results indicate that pinacidil induces a glibenclamide-sensitive Kcurrent through only one type of K+ channel (KATP channel) in pig urethra.