Molecular composition of 4-aminopyridine-sensitive voltage-gated K+ channels of vascular smooth muscle

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)-sen sitive, delayed rectifier Kv current of rabbit portal vein (RPV) myocytes d emonstrates similar 4-AP sensitivity and biophysical properties to Kv1 alph a -containing channels. To identify the molecular constituents underlying t he 4-AP-sensitive Kv current of vascular myocytes, we characterized the exp ression pattern of Kv1 alpha subunits and their modulatory Kv beta subunits in RPV. The mRNAs encoding pore-forming subunits Kv1.2, Kv1.4, and Kv1.5 w ere detected by reverse transcriptase-polymerase chain reaction (RT-PCR), w hereas Kv1.1, Kv1.3, and Kv1.6 transcripts were undetectable. Kv beta1.1, b eta1.2, beta1.3, beta2.1, and beta2.2 messages were expressed, whereas Kv b eta3.1 and beta4 mRNAs were undetected by RT-PCR. Kv1.2, Kv1.4, Kv1.5, Kv b eta1.2, beta1.3, and beta2.1 proteins were detected in RPV by Western blott ing and/or immunocytochemistry of freshly isolated myocytes. We provide the first evidence, from coimmunoprecipitation studies, for the formation of h eteromultimeric Kv channel complexes composed of Kv1.2, Kv1.5, and Kv beta1 .2 subunits in vascular smooth muscle.