Loss of potassium ion channels in the cerebral circulation of hypertensive rats: Membrane associated proteins and myogenic tone

摘要

The Shaker-type K+ (Kv1) channels are heterotetramers composed of alpha1.2 and alpha1.5, which mediate vasodilation of cerebral circulation. This thesis project pursued three hypotheses to define several key processes that influence Kv1 channel function and expression levels in cerebrovascular smooth muscle cells (cVSMCs) of rat.;We first hypothesized that the ancillary Kvbeta2 subunits that complex with alpha1 pore-forming subunits, promote the basal expression of functional Kv1 channels in the cVSMCs of rat. In support of the hypothesis, lowering the expression of Kvbeta2 subunits using Kvbeta2---specific morpholino antisense concomitantly reduced the expression of alpha1.2 subunits in cerebral arteries, and also reduced the contribution of Kv1 channels to the resting membrane potential and resting diameter of isolated, pressurized cerebral arteries. Second, we hypothesized that a down-regulation of functional Kv1 channels contributes to the elevated cerebrovascular tone of hypertensive rats and that this event is associated with a loss of ancillary Kvbeta2 subunits. Using spontaneously hypertensive rat (SHR) and aortic-banded (Ao-B) rat models, we report that a loss of Kv1 channel dilator function and expression as a result of transcriptional down-regulation of pore-forming alpha subunit(s) contribute to the elevated cerebrovascular tone in hypertensive rats. Further, the deficiency of Kv1 channels was associated with a post-transcriptional down-regulation of Kvbeta2 subunits.;Subsequent studies demonstrated for the first time that PSD 95 ( Post Synaptic Density 95), a well characterized molecular scaffold in neurons is expressed at the surface of cVSMCs and complexes with alpha1.2 pore-forming subunits in rat cerebral arteries. Further, we hypothesized that the Kv1 channels mediate the expression of PSD 95 in rat cerebral arteries and that the loss of Kv1 channels in cerebral arteries of hypertensive rats is associated with a down-regulation of the PSD 95 scaffolds. In support of the hypothesis, the knockdown of alpha1 subunits using specific siRNAs concomitantly reduced PSD 95 expression in rat cerebral arteries. Furthermore, a post-transcriptional loss of PSD 95 was observed in cerebral arteries of SHR and Ao-B rats.;Collectively, this thesis provide evidence for a dynamic interplay between Kv1 channels, ancillary Kvbeta2 subunits and PSD 95 scaffolds in rat cerebral arteries.