Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Physiology and Pharmacology
Supervisor
Welsh, Donald G.
Abstract
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.
Summary for Lay Audience
Sustaining life in the human body relies on maintaining a balance between oxygen requirements by tissues and delivery executed by arteries carrying blood from the heart to body organs. This is a fundamental process that if disrupted can lead to tissue injury and possibly death. While important, the precise subcellular mechanisms of how this matching happens is still not well-understood. An artery retains a layer of muscle cells that reduces its diameter when these cells contract in response to increased pressure to stabilize delivery. The amount of calcium inside these muscle cells controls how much they are contracted, and accordingly the diameters of the arteries, a major determinant of blood pressure. Calcium enters these cells through specific channels of which one called CaV1.2 is extensively researched. We propose another channel called CaV3.1 to be also critical in certain scenarios and show that it can control arterial diameter by causing waves of calcium increases inside cells of the muscle layer. Other tiny blood vessels within organs, called capillaries, can also regulate their own blood supply by sending signals of need to the upstream arteries causing increases in their diameters, hence more delivery, matching demand with supply. Our work also investigates the control of oxygenation through signals originating in capillaries, within which red blood cells release oxygen to tissues, and when tissue demand rises, more oxygen is released from red blood cells accordingly. This is accompanied by the release of other molecules, of note, ATP, to which capillaries respond by sending electrical signals to arterioles decreasing calcium in their muscle cells thereby increasing their diameters. In this pathway, we identified two key proteins named KATP and P2X4R which convey the electrical signals. Reducing KATP activity in tissues other than blood vessels bears therapeutic importance, hence our research begins to explain why marketed drugs which inhibit their activity can have severe, possibly fatal side effects. By investigating these mechanisms, our research helps shape the understanding of how the human body functions, which further provides insight about the novel therapeutic tools for diseases and the optimized use of the already available ones.
Recommended Citation
El-Lakany, Mohammed A., "Reimagining Electromechanical Coupling in the Control of Arterial Tone and Capillary Blood Flow" (2025). Electronic Thesis and Dissertation Repository. 10686.
https://ir.lib.uwo.ca/etd/10686
