Hyposmotic challenge inhibits inward rectifying K+ channels in cerebral arterial smooth muscle cells

Hyposmotic challenge inhibits inward rectifying K+ channels in cerebral arterial smooth muscle cells. Am J Physiol Heart Circ Physiol 292: H1085 - H1094, 2007. First published October 20, 2006; doi: 10.1152/ajpheart. 00926.2006. - This study sought to define whether inward rectifying K+ (K-IR) channels were modulated by vasoactive stimuli known to depolarize and constrict intact cerebral arteries. Using pressure myography and patch-clamp electrophysiology, initial experiments revealed a Ba2+-sensitive K-IR current in cerebral arterial smooth muscle cells that was active over a physiological range of membrane potentials and whose inhibition led to arterial depolarization and constriction. Real-time PCR, Western blot, and immunohistochemical analyses established the expression of both K(IR)2.1 and K(IR)2.2 in cerebral arterial smooth muscle cells. Vasoconstrictor agonists known to depolarize and constrict rat cerebral arteries, including uridine triphosphate, U46619, and 5-HT, had no discernable effect on whole cell K-IR activity. Control experiments confirmed that vasoconstrictor agonists could inhibit the voltage-dependent delayed rectifier K+ (K-DR) current. In contrast to these observations, a hyposmotic challenge that activates mechanosensitive ion channels elicited a rapid and sustained inhibition of the K-IR but not the K-DR current. The hyposmotic-induced inhibition of K-IR was 1) mimicked by phorbol-12-myristate-13-acetate, a PKC agonist; and 2) inhibited by calphostin C, a PKC inhibitor. These findings suggest that, by modulating PKC, mechanical stimuli can regulate K-IR activity and consequently the electrical and mechanical state of intact cerebral arteries. We propose that the mechanoregulation of K-IR channels plays a role in the development of myogenic tone.