Hypertension is a risk factor for
cerebrovascular diseases, including
stroke and
dementia. During
hypertension, arteries become constricted and are less responsive to
vasodilators, including
nitric oxide (NO). The regulation of arterial contractility by smooth muscle cell (myocyte) large-conductance
calcium (Ca2+)-activated
potassium (
BK) channels is altered during
hypertension, although mechanisms involved are unclear. We tested the hypothesis that dysfunctional trafficking of pore-forming
BK channel (BKα) and auxiliary β1 subunits contributes to changes in cerebral artery contractility of
stroke-prone spontaneously hypertensive rats (SP-SHRs). Our data indicate that the amounts of total and surface BKα and β1
proteins are similar in unstimulated arteries of age-matched SP-SHRs and normotensive Wistar-Kyoto rats. In contrast, stimulated surface-trafficking of β1 subunits by NO or membrane depolarization is inhibited in SP-SHR myocytes. PKCα (
protein kinase C α) and PKCβII total
protein and activity were both higher in SP-SHR than in Wistar-Kyoto rat arteries. NO or depolarization robustly activated Rab11, a small trafficking
GTPase, in Wistar-Kyoto rat arteries but weakly activated Rab11 in SP-SHRs.
Bisindolylmaleimide, a PKC inhibitor, and overexpression of a PKC phosphorylation-deficient Rab11A mutant (Rab11A S177A) restored stimulated β1 subunit surface-trafficking in SP-SHR myocytes.
BK channel activation by NO was inhibited in SP-SHR myocytes and restored by Rab11A S177A expression. Vasodilation to NO and
lithocholate, a BKα/β1 channel activator, was inhibited in pressurized SP-SHR arteries and reestablished by
bisindolylmaleimide. In summary, data indicate that spontaneously active PKC inhibits Rab11A-mediated β1 subunit trafficking in arterial myocytes of SP-SHRs, leading to dysfunctional NO-induced
BK channel activation and vasodilation.