Pharmacological and molecular evidence for the involvement of K v4.3 in ultra-fast activating K + currents in murine portal vein myocytes

Abstract

Background and purpose:The aim of this study was to determine the molecular identity of a transient K + current (termed I UF) in mouse portal vein myocytes using pharmacological and molecular tools. Experimental approach: Whole cell currents were recorded using the ruptured patch con from either acutely dispersed single smooth muscle cells from the murine portal vein or human embryonic kidney cells. Reverse transcriptase polymerase reaction (RT-PCR) experiments were undertaken on RNA isolated from mouse portal vein using primers specific for various voltage-dependent K + channels, auxillary subunits and calcium-binding proteins. Immunocytochemistry was undertaken using an antibody specific for K v4.3. Key results: I UF had a mean amplitude at +40 mV of 558 ± 50 pA (n = 32) with a mean time to peak at +40 mV of ∼4 ms. I UF activated and inactivated with a half maximal voltage of -12 ± 2 mV and -85 ± 2 mV, respectively. I UF was relatively resistant to 4-aminopyridine (5 mM produced 30 ± 6% block at +20 mV) but was inhibited effectively by flecainide (IC 50 value was 100nM) and phrixotoxin II. This pharmacological profile is consistent with I UF being comprised of K v4.x proteins and this is supported by the results from the quantitative PCR and immunocytochemical experiments. Conclusions and implications: These data represent a rigorous investigation of the molecular basis of vascular transient K + currents and implicates K v4.3 as a major component of the channel complex. © 2006 Nature Publishing Group. All rights reserved.