Abstract

Proximal tubular reabsorption is of primary importance in the regulation of the homeostasis of inorganic sulfate, an electrolyte that is necessary for biosynthetic and detoxification reactions. The objective of the present investigation was to determine the effect of dietary sulfate deprivation, produced by a diet low in methionine, on the renal transport of sulfate. Female Lewis rats were fed a diet containing negligible amounts of sulfate and cystine and low in methionine (0.37%) or a control diet (methionine 1.12%, cystine 0.07%) for 8 days to examine the urinary excretion rate and renal clearance of sulfate. The sulfate excretion rate was decreased by day 4 of the low methionine diet and remained low. Both the urinary excretion rates and renal clearance values were significantly decreased on day 8 (144 +/- 71 vs. 517 +/- 264 mumol/12 hr in controls, mean +/- S.D., n = 7, P < .005 and 0.38 +/- 0.19 vs. 1.07 +/- 0.61 ml min-1 kg-1 in controls, n = 5-6, P < .05, respectively), although the serum sulfate concentrations were unchanged. In vitro transport studies were performed in kidney cortex brush border membrane (BBM) and basolateral membrane vesicles isolated from rats fed either the low methionine or control diet for 7 to 9 days. The Vmax for BBM sodium/sulfate cotransport was increased in kidneys from animals that received the low methionine diet (1.1 +/- 0.10 vs. 0.75 +/- 0.08 nmol mg of protein-1 10 sec-1 in controls, n = 5, P < .001); there were no significant differences in the Km.(ABSTRACT TRUNCATED AT 250 WORDS)