Increased flow induces a series of vascular responses, the earliest of which are prodilatory and largely endothelial mediated, followed by the development of myogenic tone (which serves to return blood flow towards baseline) and enhanced reactivity to agonists. The mechanisms, which underlie this heightened response to contractile agents, are incompletely understood, but likely involve ion channel-mediated transduction of signals in endothelial and vascular smooth muscle cells. We have developed a model of high flow to isolated lung lobes of young pigs (created by an aorto-pulmonary anastomosis) which results in neointimal proliferation characteristic of clinical pulmonary hypertension and early enhanced reactivity which reactivity appears to be endothelial and L-type calcium channel dependent. Our preliminary data suggest that sustained flow results in increased expression of voltage-gated calcium channels and dysfunctions in NOS which may contribute to enhanced reactivity of shunted arteries. We hypothesize that acutely enhanced synthesis of endothelial-derived EETs increases opening of L-type calcium and decreases the opening of calcium activated K channels in subjacent PAVSMs following increased flow.
The specific aims of the grant are threefold: (i) We will identify the contribution of the endothelial second messenger signaling pathways including PLC, EETs, NOS and Ca(L) and KCa ion channels in vascular smooth muscle cells to the tone and reactivity of PAs exposed to high or baseline flows. (2) We will characterize flow-induced changes in expression of eNOS levels in PAs as well as expression of Ca(L) and KCa type ion channels in pulmonary artery vascular smooth muscle cells. (3) We will examine flow-induced changes in activity of endothelial second messenger signaling cascades PLC, EETs, NOS, gating of Ca(L) and KCa channels in PAVSM, and effect of EETs on [Ca2+]i in PAVSMCs of shunted versus non-shunted pulmonary arteries. These studies should yield valuable information about cellular mechanisms which underlie high flow induced vasculopathy, which conditions complicate a number of clinically important conditions such as repair of congenital heart defects, pneumonectomies, and others. ? ?
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