Reimagining Electromechanical Coupling in the Control of Arterial Tone and Capillary Blood Flow

Efficient tissue perfusion relies on precise O2 demand-supply matching, whereby vascular responses to signals originating in tissues, arteries or capillaries optimize flow delivery. Electrical charges across membranes of vascular smooth muscles define their contractility, termed electromechanical coupling, novel control of which is interrogated herein in two parts: First, CaV3.1 channels and tone development, and second, capillary-to-arteriole conduction mediating O2 signals in the microvasculature. The arterial myogenic response involves smooth muscle contraction to intraluminal pressure, wherein Ca2+ influx through voltage-gated Ca2+ channels, primarily L-type (CaV1.2), is pivotal. Other Ca2+ channels expectedly dominate when CaV1.2 activity drops at hyperpolarized membrane potentials. Using mesenteric arteries from C57BL/6 and CaV3.1-/- mice, we demonstrate that CaV3.1 channels facilitate myogenic tone development at hyperpolarized voltages through IP3R-mediated Ca2+ waves. This mechanism is linked to systemic blood pressure regulation, emphasizing CaV3.1 as a therapeutic target. Capillary-to-arteriole conducted signalling partly fosters O2 demand-supply matching, importantly in skeletal muscle where RBC-released ATP during O2 desaturation theoretically hyperpolarizes capillary endothelial cells (cECs). In vivo imaging in anesthetized C57BL/6 mice monitored capillary hemodynamics and RBC O2 saturation (SO2) in exteriorized skeletal muscle (EDL), situated overtop a gas chamber, in which a drop in O2 reduces capillary RBC SO2 and augments RBC supply rate. Findings postulate that P2X4 receptors (P2X4Rs), and ATP-sensitive K+ channels (KATP) mediate a novel pathway for conducted O2 signalling, evidenced by diminished capillary hemodynamic responses to low O2 following EDL incubation with selective blockers of KATP (glyburide) or P2X4R (5-BDBD). Immunofluorescence and patch-clamp electrophysiology confirmed functional expression of Kir6.1 subunits and P2X4Rs in EDL capillaries, revealing K+ currents in cECs that are pinacidil-activated, glyburide-sensitive, and ATP-γ-S-activated, 5-BDBD-sensitive. Speculatively, KATP inhibition and demand-supply decoupling constitutes a possible mechanism for the cardiac side effects of sulfonylureas, supported by computer modelling of human cardiac tissue. Results dismissed the involvement of other K+ channels, P1 receptors, or nitric oxide bioactivity in observed responses. Nevertheless, endothelial nitric oxide synthase bioactivity maintains baseline RBC flux for adequate oxygenation. Together, this work establishes novel molecular mechanisms underlying vascular responses to pressure and O2, offering insights into therapeutic strategies for blood pressure control and tissue oxygenation.