MYO-INOSITOL TRANSPORT IN SLICES OF RAT KIDNEY CORTEX .2. EFFECT OF IONIC COMPOSITION OF MEDIUM

The effect of changes in the ionic composition of the incubation medium on the active uptake and retention of myo-inositol by cortex slices from rat kidneys has been assessed. The Na+ requirement could not be satisfied by Li+, K+, Rb+, Cs+, choline+ or Tris+. K+ (>4 mM) was necessary for optimal uptake and retention of inositol, but could be replaced completely with Rb+, Cs+ was only partly effetive in place of K+, whereas Li+ and NH4+ were ineffective. The effects on inositol uptake and leakage produced by the substitution of choline+ for Na+ were largely reversible, indicating that choline had not permanently damaged the slices. Neither glucose nor ATP restored the values of the two parameters examined to normal in the absence of K+ or at low levels of Na+. Na+ alone was not able to maintain the integrity of the system. Both Ca2+ and Mg2+ at optimal concentrations of 1 mM and 1-2 mM, respectively, were required, but could be replaced by Sr2+ concentrations as low as 0.75 mM. The inhibition of inositol uptake by ouabain in Krebs-Ringer bicarbonate media also occurred, when K+ was either omitted or replaced by other monovalent cations. It was partly prevented by increased concentrations of K+, Cs+ or, especially, Rb+, but not by Ca2+. The effects of cations are discussed in terms of the mechanism of active transport of non-electrolytes and cations and of the integrity of renal tubular membranes. © 1969.