Received January 15, 2007
Revised January 22, 2007
Accepted after revision February 12, 2007

¹ Institute of Basic Medical Sciences, Medical College, Dalian University
² Department of Physiology, Xinxiang Medical College, Xinxiang 453003, China

^* To whom correspondence should be addressed. E-mail: zhouss{at}dlu.edu.cn.

	Abstract

The effects of monocarboxylic acid-derived Cl^- channel blockers on cardiac depolarization-activated K⁺ currents were investigated. Membrane currents in rat ventricular myocytes were recorded using the whole-cell configuration of the patch-clamp technique. 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and niflumic acid (NFA) induced an outward current at 0 mV. NPPB and NFA failed to induce any current when used intracellularly or after K⁺ in the bath and pipette solutions was replaced by equimolar Cs⁺. Voltage pulse protocols revealed that NPPB and NFA enhanced the steady-state K⁺ current but inhibited the transient outward K⁺ current. Genistein, a tyrosine kinase (PTK) inhibitor, inhibited NPPB- and NFA-induced outward current. Another PTK inhibitor, lavendustin A, produced a comparable effect. In contrast, the inactive analogue of genistein, daidzein, was ineffective. Orthovanadate, a tyrosine phosphatase inhibitor, markedly slowed the deactivation of the outward current induced by NPPB and NFA. H-89, a PKA inhibitor, inhibited NPPB-induced outward current at 0 mV. In contrast, the PKC inhibitor H-7 was without significant effect on the action of NPPB. Pretreating the myocytes with genistein or H-89 prevented the enhancing effect of NPPB. Increasing intracellular Cl^- from 22 to 132 mM slightly reduced NPPB-induced outward current at 0 mV. These results demonstrate that the monocarboxylic acid-derived Cl^- channel blockers NPPB and NFA enhance cardiac steady-state K⁺ current, and suggest that the enhancing effect of the Cl^- channel blockers is mediated by stimulation of PKA and PTK signaling pathways.

Key Words: Cardiac muscle, Chloride channel, Potassium current