Metabolism of Isolated Kidney Tubules

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Abstract
Kidney-cortex tubule suspensions were prepared by collagenase treatment of kidney cortex from fed and starved rats. This preparation, consisting mainly of proximal convoluted tubules was incubated with 3 major renal substrates, L-lactate, glutamine and oleate, to study the dose dependence of substrate uptake rates from medium substrate combinations. All 3 substances, when added at near physiological concentrations, modified the uptake rate and fate of the other substrates. Oleate inhibited lactate uptake and lactate decreased glutamine metabolism. Glutamine led to a marked increase in lactate uptake. Both glutamine and lactate increased oleate metabolism. Glucose was the main product of lactate and glutamine metabolism, lactate being preferentially taken up for this process. Oleate led to a net synthesis of triglycerides in the tubules, which was stimulated by the addition of lactate and glutamine. More than 75% of the oleate taken up was recovered as triglycerides. In the absence of fatty acids, triglyceride content of tubules decreased. Oleate may be taken up in preference to lactate and glutamine when all 3 substrates are offered to the tubule. Glucose and triglycerides are the main metabolic products of tubular substrate metabolism. Whereas glucose is released into the medium, triglycerides are stored in the tubule cell.

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