Voltage-gated K+ channels in rat small cerebral arteries:: molecular identity of the functional channels

Voltage-gated potassium (K-V) channels represent an important dilator influence in the cerebral circulation, but the composition of these tetrameric ion channels remains unclear. The goals of the present study were to evaluate the contribution of K(V)1 family channels to the resting membrane potential and diameter of small rat cerebral arteries, and to identify the a-subunit composition of these channels using patch-clamp, molecular and immunological techniques. Initial studies indicated that 1 mumol l(-1) correolide (COR), a specific antagonist of K(V)1 channels, depolarized vascular smooth muscle cells (VSMCs) in pressurized (60 mmHg) cerebral arteries from -55 +/- 1 mV to -34 +/- 1 mV, and reduced the resting diameter from 152 +/- 15 mum to 103 +/- 20 mum. In patch clamped VSMCs from these arteries, COR-sensitive K(V)1 current accounted for 65% of total outward K-V current and was observed at physiological membrane potentials. RT-PCR identified mRNA encoding each of the six classical K(V)1 alpha-subunits, K(V)1.1-1.6, in rat cerebral arteries. However, only the K(V)1.2 and 1.5 proteins were detected by Western blot. The expression of these proteins in VSMCs was confirmed by immunocytochemistry and co-immunoprecipitation of K(V)1.2 and 1.5 from VSMC membranes suggested K(V)1.2/1.5 channel assembly. Subsequently, the pharmacological and voltage-sensitive properties of K(V)1 current in VSMCs were found to be consistent with a predominant expression of K(V)1.2/1.5 heterotetrameric channels. The findings of this study suggest that K(V)1.2/1.5 heterotetramers are preferentially expressed in rat cerebral VSMCs, and that these channels contribute to the resting membrane potential and diameter of rat small cerebral arteries.