Abstract
The aim of this study was to determine the molecular identity of a transient K+ current (termed IUF) in mouse portal vein myocytes using pharmacological and molecular tools. 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 Kv4.3. IUF had a mean amplitude at +40 mV of 558 +/- 50 pA (n = 32) with a mean time to peak at +40 mV of approximately 4 ms. IUF activated and inactivated with a half maximal voltage of -12 +/- 2 mV and -85 +/- 2 mV, respectively. IUF was relatively resistant to 4-aminopyridine (5 mM produced 30 +/- 6 % block at +20 mV) but was inhibited effectively by flecainide (IC50 value was 100 nM) and phrixotoxin II. This pharmacological profile is consistent with IUF being comprised of Kv4.x proteins and this is supported by the results from the quantitative PCR and immunocytochemical experiments. These data represent a rigorous investigation of the molecular basis of vascular transient K+ currents and implicates Kv4.3 as a major component of the channel complex.
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