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Abstract

The effects of various metabolic inhibitors on isotonic fluid absorption (J_V) in rat proximal tubules and on the Na⁺−K⁺-ATPase of isolated cell membranes of rat kidney cortex were investigated by the shrinking split oil droplet technique and biochemical methods respectively.

Both Oligomycin (5×10⁻⁵M, 10⁻⁴M) and Antimycin A (10⁻⁵M, 10⁻⁴M) inhibited isotonic fluid absorption by 80% when applied intratubularly but only in conjunction with bovine serum albumin. At these concentrations they inhibited a Na⁺−K⁺ activated adenosine triphosphate phosphohydrolase (Na⁺−K⁺ ATPase E.C. 3.6.1.3.) of cell membranes isolated from rat kidney cortex by 77%, 82% and 55%, 95%, respectively.

Sodium phosphoenolpyruvate (PEP) 5×10⁻³ M could partially reverse the inhibition of the isotonic fluid absorption but only with 10⁻⁵M Antimycin A when the Na⁺−K⁺ ATPase inhibition was apparently small.

The uncoupler, carbonyl cyanide m-chlorophenyl hydrazone (CCCP) (10⁻³M), as well as sodium cyanide (5×10⁻³M) inhibited J_V 100%, but only when applied through peritubular blood capillary perfusion.

From these findings it was concluded thatall proximal tubular isotonic fluid absorption is supported by energy fromoxidative processes, and that in a least 80% of this sodium reabsorption, ATP from oxidative phosphorylation is directly involved, while, for the remaining 20% non ATP energy is responsible.