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

Sulayma Albarwani*, Leah T. Nemetz†, Jane A. Madden‡, Ann A. Tobin†, Sarah K. England§, Phillip F. Pratt† and Nancy J. Rusch†

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_V1 family channels to the resting membrane potential and diameter of small rat cerebral arteries, and to identify the -subunit composition of these channels using patch-clamp, molecular and immunological techniques. Initial studies indicated that 1 µmol l^-1 correolide (COR), a specific antagonist of K_V1 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 µm to 103 ± 20 µm. In patch clamped VSMCs from these arteries, COR-sensitive K_V1 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_V1 -subunits, K_V1.1-1.6, in rat cerebral arteries. However, only the K_V1.2 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_V1.2 and 1.5 from VSMC membranes suggested K_V1.2/1.5 channel assembly. Subsequently, the pharmacological and voltage-sensitive properties of K_V1 current in VSMCs were found to be consistent with a predominant expression of K_V1.2/1.5 heterotetrameric channels. The findings of this study suggest that K_V1.2/1.5 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.

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