A-272651, a nonpeptidic blocker of large-conductance Ca 2+- activated K + channels, modulates bladder smooth muscle contractility and neuronal action potentials

Abstract

Background and Purpose: The large-conductance Ca 2+-activated K + channel (BK Ca, K Ca1.1) links membrane excitability with intracellular Ca 2+ signaling and plays important roles in smooth muscle contraction, neuronal firing, and neuroendocrine secretion. This study reports the characterization of a novel BK Ca channel blocker, 2,4-dimethoxy-N-naphthalen-2-yl-benzamide (A-272651). Experimental Approach: 86Rb + efflux in HEK-293 cells expressing BK Ca was measured. Effects of A-272651 on BK Ca α- and BK Ca αβ1-mediated currents were evaluated by patch-clamp. Effects on contractility were assessed using low-frequency electrical field stimulated pig detrusor and spontaneously contracting guinea pig detrusor. Effects of A-272651 on neuronal activity were determined in rat small diameter dorsal root ganglia (DRG). Key Results: A-272651 (10 μM) inhibited 86Rb + efflux evoked by NS-1608 in HEK-293 cells expressing BK Ca currents. A-272651 concentration-dependently inhibited BK Ca currents with IC 50 values of 4.59 μM (Hill coefficient 1.04, measured at +40 mV), and 2.82 μM (Hill coefficient 0.89), respectively, for BK Ca α and BK Ca αβ1-mediated currents. Like iberiotoxin, A-272651 enhanced field stimulated twitch responses in pig detrusor and spontaneous contractions in guinea pig detrusor with EC 50 values of 4.05±0.05 and 37.95±0.12 μM, respectively. In capsaicin-sensitive DRG neurons, application of A-272651 increased action potential firing and prolonged action potential duration. Conclusions and Implications: These data demonstrate that A-272651 modulates smooth muscle contractility and neuronal firing properties. Unlike previously reported peptide BK Ca blockers, A-272651 represents one of the first small molecule BK Ca channel blockers that could serve as a useful tool for further characterization of BK Ca channels in physiological and pathological states. © 2007 Nature Publishing Group All rights reserved.