Mesangial cells are hormone responsive cells of the glomeruli which produce prostaglandins and undergo contraction. This tissue is believed to be an important regulator of medullary blood flow and hemodynamic effects of vasopressin. Hypertrophy of this tissue has also been observed in certain disease states including diabetes. Primary cultures of rat kidney mesangial cells have recently been characterized. In these cultures, vasopressin activates phosphatidylinositol (PI) turnover resulting in elevation of inositol trisphosphate and diacylglycerol and release of calcium from internal stores. Elevation of cytosolic calcium also occurs in response to angiotensin II. Activation of a PI specific phospholipase C is an early event in response to vasopressin in this tissue and there is evidence in other tissues that a GTP binding protein tranduces this signal from the receptor. There is also evidence that the phosphatidylinositol kinases which phosphorylate PI to phosphatidylinositol- 4-phosphate (PIP) and phosphatidylinositol- 4,5-bisphosphate (PIP2) are also activated to produced more substrate for inositol trisphosphate production. We have characterized these enzymes in other tissues and found three different PI kinases and two distinct PIP kinases. In fibroblasts, addition of platelet derived growth factor (PDGF) stimulates PI turnover and causes one of the PI kinases (type I) to associate with a lectin binding protein and to become precipitable by an antibody against phosphotyrosine. These results suggest that this PI kinase becomes associated with the PDGF receptor upon PDGF binding. The goal of this proposal is to characterize the PI and PIP kinases in the mesangial cells and compare them to the enzymes previously characterized in fibroblasts brain and red cells. In particular we wish to determine whether the type I PI kinase exists in this tissue and whether vasopressin and other hormones which affect PI turnover induce changes in this enzyme analogous to those seen in response to PDGF in fibroblasts. It is hoped that this research will suggest direct biochemical mechanisms for propogation of signals from the hormone receptor to the enzyme involved in PI turnover.
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