Vasoplegia in sepsis depends on the vascular system, vasopressor, and time-point: a comparative evaluation in vessels from rats subjected to the cecal ligation puncture model.

We evaluated the effects of phenylephrine, norepinephrine, angiotensin II, and vasopressin in mesenteric, renal, carotid, and tail arteries, and in perfused mesenteric vascular bed from rats subjected to the cecal ligation and puncture (CLP) model of sepsis. Phenylephrine and angiotensin II were less efficacious in mesenteric arteries from the CLP 6 h and CLP 18 h groups than in preparations from non-septic animals, but no differences were found for norepinephrine and vasopressin between the preparations. In renal arteries, none of the vasoconstrictors had impaired activity in the CLP groups. Nonetheless, carotid arteries from the CLP 18 h group presented reduced reactivity to all vasoconstrictors tested, but only phenylephrine and norepinephrine had their effects reduced in carotid arteries from the CLP 6 h group. Despite the reduced responsiveness to phenylephrine, tail arteries from septic rats were hyperreactive to vasopressin and norepinephrine at 6 h and 18 h after the CLP surgery, respectively. The mesenteric vascular bed from CLP groups was hyporeactive to phenylephrine, norepinephrine, and angiotensin II, but not to vasopressin. The vascular contractility in sepsis varies from the well-described refractoriness, to unaltered or even hyperresponsiveness to vasoconstrictors, depending on the vessel, the vasoactive agent, and the time period evaluated.

Vasodilators activate the anion channel TMEM16A in endothelial cells to reduce blood pressure.

Systemic blood pressure is acutely controlled by total peripheral resistance as determined by the diameter of small arteries and arterioles, the contractility of which is regulated by endothelial cells lining the lumen of blood vessels. We investigated the physiological functions of the chloride (Cl-) channel TMEM16A in endothelial cells. TMEM16A channels generated calcium (Ca2+)-activated Cl- currents in endothelial cells from control (TMEM16Afl/fl) mice that were absent in those from mice with tamoxifen-inducible, endothelial cell-specific knockout of TMEM16A (TMEM16A ecKO). TMEM16A currents in endothelial cells were activated by the muscarinic receptor agonist acetylcholine and an agonist of the Ca2+ channel TRPV4, which localized in nanoscale proximity with TMEM16A as assessed by single-molecule localization imaging of endothelial cells. Acetylcholine stimulated TMEM16A currents by activating Ca2+ influx through surface TRPV4 channels without altering the nanoscale properties of TMEM16A and TRPV4 surface clusters or their colocalization. In pressurized arteries, activation of TMEM16A channels in endothelial cells induced by acetylcholine; TRPV4 channel stimulation; or intraluminal ATP, another vasodilator, produced hyperpolarization and dilation. Furthermore, deficiency of TMEM16A channels in endothelial cells resulted in increased systemic blood pressure in conscious mice. These data indicate that vasodilators stimulate TRPV4 channels, leading to Ca2+-dependent activation of nearby TMEM16A channels in endothelial cells to produce arterial hyperpolarization, vasodilation, and reduced blood pressure. Thus, TMEM16A is an anion channel in endothelial cells that regulates arterial contractility and blood pressure.

Vasodilators activate TMEM16A channels in endothelial cells to reduce blood pressure.

Endothelial cells (ECs) regulate vascular contractility to control regional organ blood flow and systemic blood pressure. Several cation channels are expressed in ECs which regulate arterial contractility. In contrast, the molecular identity and physiological functions of anion channels in ECs is unclear. Here, we generated tamoxifen-inducible, EC-specific TMEM16A knockout ( TMEM16A ecKO) mice to investigate the functional significance of this chloride (Cl - ) channel in the resistance vasculature. Our data demonstrate that TMEM16A channels generate calcium-activated Cl - currents in ECs of control ( TMEM16A fl/fl ) mice that are absent in ECs of TMEM16A ecKO mice. Acetylcholine (ACh), a muscarinic receptor agonist, and GSK101, a TRPV4 agonist, activate TMEM16A currents in ECs. Single molecule localization microscopy data indicate that surface TMEM16A and TRPV4 clusters locate in very close nanoscale proximity, with ∼18% exhibiting overlap in ECs. ACh stimulates TMEM16A currents by activating Ca 2+ influx through surface TRPV4 channels without altering the size or density of TMEM16A or TRPV4 surface clusters, their spatial proximity or colocalization. ACh-induced activation of TMEM16A channels in ECs produces hyperpolarization in pressurized arteries. ACh, GSK101 and intraluminal ATP, another vasodilator, all dilate pressurized arteries through TMEM16A channel activation in ECs. Furthermore, EC-specific knockout of TMEM16A channels elevates systemic blood pressure in conscious mice. In summary, these data indicate that vasodilators stimulate TRPV4 channels, leading to Ca 2+ -dependent activation of nearby TMEM16A channels in ECs to produce arterial hyperpolarization, vasodilation and a reduction in blood pressure. We identify TMEM16A as an anion channel present in ECs that regulates arterial contractility and blood pressure. One sentence summary: Vasodilators stimulate TRPV4 channels, leading to calcium-dependent activation of nearby TMEM16A channels in ECs to produce arterial hyperpolarization, vasodilation and a reduction in blood pressure.