Control of microvascular function by ion channels

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Activation of post-junctional neurotransmitter receptors in vascular endothelial and smooth muscle cells modulates vascular tone and causes significant alterations in organ perfusion, mechanisms of which may be amplified or diminished in cardiovascular and kidney disease. Neurotransmitter release from presynaptic nerve terminals is highly dependent on extracellular Ca2+ influx. Thus, modulation of Ca2+-permeable channels in neurons that impinge on microvessels can alter microcirculation by regulating neurotransmission. A large body of literature has elucidated the role of endothelial and smooth muscle Ca2+-permeable channels in the control of microvascular function. However, the physiology and pathophysiology of perivascular nerve ion channels in microcirculation are poorly understood. Accumulating evidence suggests that the transient receptor potential melastatin 8 (TRPM8), a cold-sensitive neuronal channel may exert multiple functions in other cells and tissues, including blood vessels. The current application stems from pilot studies that uncovered a new vascular role for TRPM8. Our data suggest that a subset of perivascular sympathetic nerves (sn) expresses functional and redox-sensitive TRPM8 channels. Hence, we propose to study the novel central hypothesis that snTRPM8 activation increases vascular resistance and reduces vascular bed perfusion via Ca2+-dependent catecholamine exocytosis and that this pathway contributes to the pathophysiology of reactive oxygen species in the vasculature. We will investigate whether: 1) snTRPM8 channel activation impairs vascular bed perfusion by altering microvascular diameter and 2) TRPM8- dependent sympathoexcitation contributes to oxidative stress-induced vascular dysfunction and kidney injury. This project will utilize selective pharmacological modulators of TRPM8 channels, chemical sympathectomy, and conditional and global TRPM8 knockout mouse models. Techniques to investigate microvascular function include multiphoton microscopy, myography, transit-time ultrasound, and laser-Doppler.