Membrane depolarization activates BK channels through ROCK-mediated β1 subunit surface trafficking to limit vasoconstriction

Abstract

Membrane depolarization of smooth muscle cells (myocytes) in the small arteries that regulate regional organ blood flow leads to vasoconstriction. Membrane depolarization also activates large-conductance calcium (Ca2+)–activated potassium (BK) channels, which limits Ca2+ channel activity that promotes vasoconstriction, thus leading to vasodilation. We showed that in human and rat arterial myocytes, membrane depolarization rapidly increased the cell surface abundance of auxiliary BK β1 subunits but not that of the pore-forming BKα channels. Membrane depolarization stimulated voltage-dependent Ca2+ channels, leading to Ca2+ influx and the activation of Rho kinase (ROCK) 1 and 2. ROCK1/2-mediated activation of Rab11A promoted the delivery of β1 subunits to the plasma membrane by Rab11A-positive recycling endosomes. These additional β1 subunits associated with BKα channels already at the plasma membrane, leading to an increase in apparent Ca2+ sensitivity and activation of the channels in pressurized arterial myocytes and vasodilation. Thus, membrane depolarization activates BK channels through stimulation of ROCK- and Rab11A-dependent trafficking of β1 subunits to the surface of arterial myocytes.

Endothelin-1 Stimulates Vasoconstriction Through Rab11A Serine 177 Phosphorylation

“…Membrane depolarization also stimulates an increase in surface β1 subunits, leading to BK channel activation. 12 Membrane depolarization (30 mmol/L K + ) increased surface β1 protein 3.70-fold, but did not alter surface BKα in cerebral arteries (Fig. 3A, 3B).…”

“…11 Membrane depolarization also activates BK channels by stimulating Rho kinase-mediated β1 subunit trafficking in human and rat arterial myocytes. 12 It is unclear whether vasoconstrictors inhibit BK channels and stimulate contraction by reducing the surface abundance of β1 subunits and their association with BKα. If such mechanisms exist, the processes by which vasoconstrictors decrease surface levels of β1 would be important to determine.…”

Dynamic Regulation of the Subunit Composition of BK Channels in Smooth Muscle

“…Using vertically integrated approaches, they determined that endothelin-1 stimulates PKC-dependent phosphorylation of Rab11A at serine 177, which in turn leads to decreased surface trafficking of β1 subunits, the inhibition of transient BK currents, and cerebral vasoconstriction. Interestingly, this dynamic control of BK channel subunit composition appears to function in the presence of competing stimuli (endothelin-1, nitric oxide donor, depolarization), 6, 7 supporting the idea that regulation of β1 trafficking is an important physiologic mechanism that is actively regulated by a variety of influences (see Figure). Presently, it is unclear what controls the removal of β1 subunits from BK channels.…”

“…5 Altering the subunit composition of BK channels can involve the cellular trafficking of subunits through mechanisms involving the small GTPase Rab11A. 6, 7 This GTPase controls the trafficking of ion channel subunits between endosomes and the sarcolemma of vascular smooth muscle cells.…”

“…6, 7 Previous efforts by the Jaggar laboratory have established that Rab11A regulates BK channels in nitric oxide-induced relaxation of cerebral arteries. BK channels are composed of pore-forming (α) and auxiliary (e.g., β1) subunits.…”