1,25-DIHYDROXYVITAMIN-D STIMULATES SODIUM-DEPENDENT PHOSPHATE-TRANSPORT BY RENAL OUTER CORTICAL BRUSH-BORDER MEMBRANE-VESICLES BY DIRECTLY AFFECTING MEMBRANE FLUIDITY

We examined the effects of several forms of vitamin D added to renal brush-border membrane suspensions on phosphate and glucose transport and on membrane fluidity. The 1,25-D stimulated and the other vitamin D decreased phosphate uptake. In contrast, glucose uptake was not affected by the treatment of vitamin D. The 1,25-D resulted in a significant shift of the lower transition temperature in Arrhenius plots for phosphate, but not for glucose uptakes, from 15.degree.C to 11.5.degree.C. These data indicate that the 1,25-D may alter membrane fluidity, limited to the phosphate transporter, thus affecting the phosphate uptake.