Functional Expression Profile of Voltage-Gated K+ Channel Subunits in Rat Small Mesenteric Arteries

Multiple K-v channel complexes contribute to total K-v current in numerous cell types and usually subserve different physiological functions. Identifying the complete compliment of functional K-v channel subunits in cells is a prerequisite to understanding regulatory function. It was the goal of this work to determine the complete K-v subunit compliment that contribute to functional K-v currents in rat small mesenteric artery (SMA) myocytes as a prelude to studying channel regulation. Using RNA prepared from freshly dispersed myocytes, high levels of K-v 1.2, 1.5, and 2.1 and lower levels of K-v 7.4 alpha-subunit expressions were demonstrated by quantitative PCR and confirmed by Western blotting. Selective inhibitors correolide (K-v 1; COR), stromatoxin (K-v 2.1; ScTx), and linopirdine (K-v 7.4; LINO) decreased K-v current at ? 40 mV in SMA by 46 +/- 4, 48 +/- 4, and 6.5 +/- 2 %, respectively, and K-v current in SMA was insensitive to alpha-dendrotoxin. Contractions of SMA segments pretreated with 100 nmol/L phenylephrine were enhanced by 27 +/- 3, 30 +/- 8, and 7 +/- 3 % of the response to 120 mmol/L KCl by COR, ScTX, and LINO, respectively. The presence of K-v 6.1, 9.3, beta 1.1, and beta 1.2 was demonstrated by RT-PCR using myocyte RNA with expressions of K-v beta 1.2 and K-v 9.3 about tenfold higher than K-v beta 1.1 and K-v 6.1, respectively. Selective inhibitors of K-v 1.3, 3.4, 4.1, and 4.3 channels also found at the RNA and/or protein level had no significant effect on K-v current or contraction. These results suggest that K-v current in rat SMA myocytes are dominated equally by two major components consisting of K-v 1.2-1.5-beta 1.2 and K-v 2.1-9.3 channels along with a smaller contribution from K-v 7.4 channels but differences in voltage dependence of activation allows all three to provide significant contributions to SMA function at physiological voltages.