Hypoxia is a potent physiological stimulus for contraction of pulmonary vascular smooth muscle. This response serves to balance blood flow between nonventilated and ventilated regions of the lung. With global hypoxia, as occurs in chronic obstructive lung disease, contraction of many arterial vessels produces an increase in vascular resistance and an elevation in pulmonary arterial pressure, which, if persistent produces pulmonary hypertension. Devising therapeutic strategies for this important clinical problem requires a clear understanding of the cellular mechanisms underlying the response of pulmonary artery (PA) cells to hypoxia. However, although a number of processes have been implicated, none have been clearly defined. Part of the uncertainty stems from the fact that multiple cell types can contribute to the response. Thus, the effects of low oxygen on the smooth muscle cells themselves may be obscured. The present studies will obviate these difficulties by assessing the effects of hypoxia on freshly dispersed and cultured pulmonary vascular smooth muscle cells and by comparing these responses to those seen in segments of main pulmonary artery. These studies will define the temporal relationship between the increase in contractility and changes in intracellular ion levels and in resting membrane potential. Such measurements will use the fluorescent dyes fura 2, BCECF, SBFI and B-413, to monitor cell Ca2+, H+, Na+, and membrane potential respectively. Once we define the pattern of responses to hypoxia we will examine the cellular processes that contribute to the response, assessing the possibility that the response is mediated by conventional signalling pathways (cyclic nucleotides/protein kinases, phospholipid metabolism, arachidonate) or by decreased production of reactive compounds (O2, H2O2) derived from molecular O2. Subsequent studies will examine cells and tissues from chronically hypoxic animals in which PA pressures are elevated and determine whether such tissues show persistent changes in cellular function (altered Ca2+, H+, Na+, Vm) that can explain the increased contractility of these vessels. By applying state of the art fluorescence imaging to studies on pulmonary artery cells, it should be possible to obtain valuable insights as to the cellular processes that underlie hypoxic vasoconstriction of pulmonary vascular smooth muscle.
