Hyperosmotic but not hyposmotic stress evokes a rise in cytosolic Ca2+ concentration in endothelium of intact rat aorta

Abstract

The effects of osmotic stress on the cytosolic Ca2+ concentration ([Ca2+](i)) in the endothelium of excised intact rat aorta were investigated using the indicator fura-2 and the patch clamp technique. Hyperosmotic stress evoked a reversible rise in endothelial [Ca2+](i) in the presence but not absence of extracellular Ca2+, indicating that it evoked Ca2+ entry without release from intracellular stores. Hyposmotic stress was without significant effect. Cytochalasins B and D reduced the effect of hyperosmotic stress but not acetylcholine on endothelial [Ca2+](i). In endothelium isolated from underlying smooth muscle, hyperosmotic stress produced a rise in the [Ca2+](i) and depolarisation of the endothelial membrane potential whereas hyposmotic stress was without effect. Mechanosensitive cationic channels recorded in cell-attached patches were activated by hyperosmotic solutions applied to the endothelium and inhibited by hyposmotic solutions. These data suggest that shrinkage of endothelial cells evokes an increase in [Ca2+](i) by opening a pathway for Ca2+ entry from the extracellular space. The mechanosensitive ionic channels which we have previously described may be responsible for this response.