Protein Kinase C‐Dependent TRPM4 Activation Regulates Cerebral Artery Tone

Abstract

The melastatin transient receptor potential (TRP) channel TRPM4 is a critical mediator of pressure-induced (myogenic) smooth muscle depolarization and vasoconstriction in cerebral arteries. Biophysical properties of expressed and native TRPM4 channels include activation by intracellular Ca2+ and substantial selectivity for monovalent cations. Insight into a potentially important regulatory mechanism of this channel was provided by a recent study demonstrating that protein kinase C (PKC) activity increases the sensitivity of TRPM4 to intracellular Ca2+. Further evidence supporting an important role for PKC in mediating vascular tone includes reports demonstrating that inhibition of PKC activity blunts myogenic constriction, and another study showing that intraluminal pressure enhances PKC translocation to the plasma membrane. We therefore hypothesized that PKC-dependent activation of TRPM4 contributes to pressure-induced smooth muscle depolarization and vasoconstriction in cerebral arteries. In whole-cell patch-clamp studies, a rapidly-inactivating, Ca2+-dependent, outwardly-rectifying, monovalent-selective cation current with properties similar to those of cloned TRPM4 channels was identified in freshly-isolated cerebral artery myocytes. To examine the functional relationship between TRPM4 and PKC-dependent vascular responses, TRPM4 expression was suppressed in isolated cerebral arteries using antisense oligonucleotides. Arterial myocyte depolarization and vasoconstriction induced by the PKC activator phorbol 12-myristate13-acetate (PMA) were attenuated in arteries treated with TRPM4 antisense compared with controls. We conclude that PKC-dependent phosphorylation of TRPM4 is a critical mediator of cerebral artery tone. Supported by NIH F32 HL075995 and AHA 0535226N (S. Earley) and RO1 HL58231 (J.E. Brayden).