Table of Contents:
The aim of this study was to clarify the molecular mechanisms of hypoxic pulmonary vasoconstriction in precapillary arterial pulmonary smooth muscle cells (PASMC) and ischemia-reperfusion injury in lung endothelial cells (LEC). TRPC6-activation is essential for both mechanisms, because they are abolished in TRPC6-deficient mice. To investigate the mechanisms at the cellular level PASMC and LEC were isolated and their identity confirmed by specific antibodies. Components of the signalling cascade in both cell types were identified by monitoring the Ca2+-increase in response to the application of hypoxic solutions. Important key components of the signal transduction cascades in addition to TRPC6 were identified by the application of specific inhibitors and sensors to the cells. In summary, activation of receptors by nanomolar agonist concentrations (priming) results in a low level of diacylglycerol (DAG) production, which is not able to activate TRPC6 channels, but is rapidly degraded by DAG-kinases. After application of hypoxia, however, production of reactive oxygen species results in DAG-kinase inhibition and sufficient DAGaccumulation to induce TRPC6-activation. The bulk of Ca2+ influx in PASMC responsible for contraction enters through L-type voltage gated Ca2+ channels. These are activated by the depolarisation resulting from Na+ influx through TRPC6- channels. A similar signal transduction cascade exists in LEC, although it is unclear whether a priming event is necessary. In these cells, TRPC6 channels mediate the Ca2+ influx, because L-type voltage gated calcium channels are not expressed. Therefore, TRPC6 is an important perspective pharmacological target for acute hypoxic pulmonary vasoconstriction in PASMC and ischemia-reperfusion injury in LEC.