Sarah K Burris

TMEM16A/ANO1 Channels Contribute to the Myogenic Response in Cerebral Arteries

Rationale: Pressure-induced arterial depolarization and constriction (the myogenic response) is a smooth muscle cell (myocyte)-specific mechanism that controls regional organ blood flow and systemic blood pressure. Several different nonselective cation channels contribute to pressure-induced depolarization, but signaling mechanisms involved are unclear. Similarly uncertain is the contribution of anion channels to the myogenic response and physiological functions and mechanisms of regulation of recently discovered transmembrane 16A (TMEM16A), also termed Anoctamin 1, chloride (Cl−) channels in arterial myocytes. Objective: To investigate the hypothesis that myocyte TMEM16A channels control membrane potential and contractility and contribute to the myogenic response in cerebral arteries. Methods and Results: Cell swelling induced by hyposmotic bath solution stimulated Cl− currents in arterial myocytes that were blocked by TMEM16A channel inhibitory antibodies, RNAi-mediated selective TMEM16A channel knockdown, removal of extracellular calcium (Ca2+), replacement of intracellular EGTA with BAPTA, a fast Ca2+ chelator, and Gd3+ and SKF-96365, nonselective cation channel blockers. In contrast, nimodipine, a voltage-dependent Ca2+ channel inhibitor, or thapsigargin, which depletes intracellular Ca2+ stores, did not alter swelling-activated TMEM16A currents. Pressure-induced (−40 mm Hg) membrane stretch activated ion channels in arterial myocyte cell–attached patches that were inhibited by TMEM16A antibodies and were of similar amplitude to recombinant TMEM16A channels. TMEM16A knockdown reduced intravascular pressure-induced depolarization and vasoconstriction but did not alter depolarization-induced (60 mmol/L K+) vasoconstriction. Conclusions: Membrane stretch activates arterial myocyte TMEM16A channels, leading to membrane depolarization and vasoconstriction. Data also provide a mechanism by which a local Ca2+ signal generated by nonselective cation channels stimulates TMEM16A channels to induce myogenic constriction.

Smooth muscle cell transient receptor potential polycystin-2 (TRPP2) channels contribute to the myogenic response in cerebral arteries

•  Intravascular pressure is reported to activate several mechanosensitive ion channels, leading to smooth muscle cell (SMC) depolarization, voltage‐dependent Ca2+ channel activation and vasoconstriction; a process known as the ‘myogenic response’. •  Polycystin‐1 and ‐2 (TRPP1 and ‐2) have been shown to differentially regulate the mesenteric artery myogenic response, with TRPP2 expression attenuating vasoconstriction. •  We show that TRPP2 is the major TRPP isoform expressed and that TRPP2 is located primarily in the plasma membrane in cerebral artery SMCs. •  Selective TRPP2 knockdown reduced swelling‐induced non‐selective cation currents (ICat) in SMCs and myogenic tone in cerebral arteries. •  These data indicate that TRPP2 activation contributes to the cerebral artery myogenic response and suggest that TRPP2 performs differential functions in different vascular beds.

9-Phenanthrol inhibits recombinant and arterial myocyte TMEM16A channels

In arterial smooth muscle cells (myocytes), intravascular pressure stimulates membrane depolarization and vasoconstriction (the myogenic response). Ion channels proposed to mediate pressure‐induced depolarization include several transient receptor potential (TRP) channels, including TRPM4, and transmembrane protein 16A (TMEM16A), a Ca2+‐activated Cl− channel (CaCC). 9‐Phenanthrol, a putative selective TRPM4 channel inhibitor, abolishes myogenic tone in cerebral arteries, suggesting that either TRPM4 is essential for pressure‐induced depolarization, upstream of activation of other ion channels or that 9‐phenanthrol is non‐selective. Here, we tested the hypothesis that 9‐phenanthrol is also a TMEM16A channel blocker, an ion channel for which few inhibitors have been identified.

Arterial smooth muscle cell PKD2 (TRPP1) channels control systemic blood pressure

Systemic blood pressure is determined, in part, by arterial smooth muscle cells (myocytes). Several Transient Receptor Potential (TRP) channels are proposed to be expressed in arterial myocytes, but it is unclear if these proteins control physiological blood pressure and contribute to hypertension in vivo. We generated the first inducible, smooth muscle-specific knockout for a TRP channel, namely for PKD2 (TRPP1), to investigate arterial myocyte and blood pressure regulation by this protein. Using this model, we show that intravascular pressure and α1-receptors activate PKD2 channels in arterial myocytes of different systemic organs. PKD2 channel activation in arterial myocytes leads to an inward Na+ current, membrane depolarization and vasoconstriction. Inducible, smooth muscle cell-specific PKD2 knockout lowers both physiological blood pressure and hypertension and prevents pathological arterial remodeling during hypertension. In summary, we show for the first time that arterial myocyte PKD2 channels control systemic blood pressure and targeting reduces high blood pressure.