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Journal of Experimental Biology 130,294-304 (1987)
Published by Company of Biologists 1987

Lactate Uptake by Toadfish Hepatocytes: Passive Diffusion is Sufficient

PATRICK J. WALSH 1

1 Division of Biology and Living Resources, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA

Mechanisms of hepatic lactate uptake were studied in the gulf toadfish, Opsanus beta by following the accumulation of [14C]lactate by isolated hepatocytes in vitro. Uptake rates were linear for up to 5 s at external lactate concentrations of 1 and 20 mmol l-1. 5-s uptake rates for several concentrations in the physiological range (i.e. 0.2–20 mmol l-1) yielded a linear double reciprocal plot (1/v vs 1/[lactate]) that passed through the origin. Lactate uptake was not inhibited by known inhibitors of carrier-mediated lactate transport (e.g. 5 mmol l-1 {alpha}-cyano-4-hydroxycinnamate; 10 mmol l-1 pyruvate), and was not stereospecific for l-(+)-lactate. These observations indicate that lactate uptake is by passive diffusion in toadfish hepatocytes. Lactate uptake by toadfish hepatocytes further differed from lactate uptake by mammalian tissues in that rates were not altered by changes in either pHe. (6.5–8.0) or [Na+]c (3–151 mmol l-1). Rates of lactate conversion to glucose and CO2 were measured and compared to uptake rates, and it appears that rates of lactate metabolism are not limited by passive diffusion. These results are discussed in relation to rates of lactate uptake and metabolism in mammalian hepatocytes.

Key words: lactate transport, passive diffusion, hepatocytes, Opsanus beta

Accepted on March 4, 1987


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© The Company of Biologists Ltd 1987