EFFECT OF FETAL EXPOSURE TO GENTAMICIN ON PHOSPHATE-TRANSPORT IN YOUNG-RAT KIDNEY

The renal phosphate (P(i))-transporting capacity normally increases, due to increased carrier system affinity, during the third postnatal week in rats. However, the tubular P(i) reabsorption of rat pups born from gentamicin-treated mothers does not increase during this period. This study determines whether exposure to gentamicin in utero selectively alters the postnatal maturation of the carrier affinity for P(i). P(i) and glucose transports by proximal tubule brush-border membrane (BBM) were studied. The maximal rate of uptake (V(max)) of Na-P(i) cotransport was significantly lower (536 +/- 169 pmol . mg protein-1 . 10 s-1; n = 6, P < 0.01) in gentamicin-exposed rats than in controls (1,021 +/- 167 pmol . mg protein-1 . 10 s-1, n = 6), whereas the Michaelis constant (K(m)) values were the same. Gentamicin exposure had no effect on plasma parathyroid hormone concentration or on BBM glucose transport activity. The total phospholipid content of BBM, their phospholipid composition, cholesterol content, and cholesterol-to-total phospholipid mole ratio were unaltered, suggesting that membrane fluidity was unchanged. The V(max) of BBM alkaline phosphatase was lower in gentamicin-exposed rats than in controls.