The studies designed in this proposal will examine two main areas in transport physiology: The mechanism whereby calcium is transported across the turtle bladder membrane, and the role of calcium and PTH on toad bladder transport. In turtle bladder we will examine the calcium transporting properties of the mitochondrial rich (MR) and granular (G) cells (membrane sodium NA-Ca exchange and Ca-ATPase activity). We postulate that the MR Cell contains high Ca-ATPase activity. From unidirectional calcium flux studies we further postulate that the turtle bladder has a Na-Ca exchanger on the apical membrane. Apical and basolateral vesicles will be isolated and tested for activity; if the Golgi membrane is the precursor of the apical membrane in turtle bladder as it is in toad, Golgi membranes should also exhibit Na-Ca exchange activity. In toad bladder PTH decreases membrane transport independent of cyclic AMP; PTH increases extracellular calcium uptake in isolated epithelial cells. Calcium transport in MR and G Cells will be studied in the presence and absence of PTH. We postulate that the effect of PTH on membrane transport, is not receptor mediated, and that the hormone will have no direct effect of Ca- ATPase activity or NA-Ca exchange. PTH may exert an indirect effect solely due to the increase in cell calcium. The role of PTH on cytosolic phospholipid exchange proteins will be examined as PTH may enhance their activity if extracellular calcium is not rate limiting.
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