The renal sodium-calcium exchanger.

The functional expression of the renal sodium-calcium exchanger has been amply documented in studies on renal cortical basolateral membranes. In perfused renal tubules, other investigators have shown sodium-calcium exchange activity in the proximal convolution of the rat and in the distal convolution, the connecting tubule, and the collecting tubule of the rabbit. In rat proximal tubules, we found that the sodium-calcium exchanger is an important determinant of cytosolic calcium homeostasis, since inhibition of sodium-dependent calcium efflux mode caused a large accumulation of tubular calcium. In membranes from rat proximal tubules sodium-calcium activity was high, and in intact proximal tubules, the tubular sodium-calcium exchanger exhibited a high affinity for cytosolic calcium and had a substantial transport capacity, which may be absolute requirements for the maintenance of stable cytosolic calcium in proximal tubules.