Molecular Composition of 4-Aminopyridine-Sensitive Voltage-Gated K + Channels of Vascular Smooth Muscle

Abstract

Voltage-gated K + channels (Kv) play a critical role in regulating arterial tone by modulating the membrane potential of vascular smooth muscle cells. Our previous work demonstrated that the dominant 4-aminopyridine (4-AP)-sensitive, delayed rectifier Kv current of rabbit portal vein (RPV) myocytes demonstrates similar 4-AP sensitivity and biophysical properties to Kv1α-containing channels. To identify the molecular constituents underlying the 4-AP-sensitive Kv current of vascular myocytes, we characterized the expression pattern of Kv1α subunits and their modulatory Kvβ subunits in RPV. The mRNAs encoding pore-forming subunits Kv1.2, Kv1.4, and Kv1.5 were detected by reverse transcriptase-polymerase chain reaction (RT-PCR), whereas Kv1.1, Kv1.3, and Kv1.6 transcripts were undetectable. Kvβ1.1, β1.2, β1.3, β2.1, and β2.2 messages were expressed, whereas Kvβ3.1 and β4 mRNAs were undetected by RT-PCR. Kv1.2, Kv1.4, Kv1.5, Kvβ1.2, β1.3, and β2.1 proteins were detected in RPV by Western blotting and/or immunocytochemistry of freshly isolated myocytes. We provide the first evidence, from coimmunoprecipitation studies, for the formation of heteromultimeric Kv channel complexes composed of Kv1.2, Kv1.5, and Kvβ1.2 subunits in vascular smooth muscle.