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Journal of Experimental Biology 127,373-387 (1987)
Published by Company of Biologists 1987

Membrane-Potential-Sensitive, Na⁺-Independent Lysine Transport by Lobster Hepatopancreatic Brush Border Membrane Vesicles

GREGORY A. AHEARN ¹ and LAUREL P. CLAY ¹

¹ Department of Zoology, 2538, The Mall, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA

Transport of l-[³H]lysine by epithelial brush border membrane vesicles (BBMV) of lobster hepatopancreas, formed by a magnesium precipitation technique, was insensitive to transmembrane gradients of Na⁺, K⁺, TMA⁺ or H⁺. Apparent initial lysine entry rates (15 s uptake) and extent of amino acid accumulation against a concentration gradient (overshoot) were both stimulated by transmembrane anion gradients according to the following sequence: SCN^- > Cl^- > gluconate^-. The magnitude of this anion-gradient-dependent transport was significantly increased by bilateral acidic pH. Lysine transport at acidic pH strongly responded to transmembrane potential developed by addition of valinomycin to K⁺-loaded vesicles, or was markedly reduced if K⁺-equilibrated vesicles were incubated with the ionophore in the presence of an inwardly directed SCN^- gradient. Lysine influx occurred by the combination of at least one carrier process and ‘apparent diffusion’. l-Arginine, l-alanine and l-leucine, added to the external medium, were all strong inhibitors of lysine influx. The first two were competitive inhibitors of lysine entry, while the latter was non-competitive in effect. These results suggest that lysine, arginine and alanine may share a common, Na⁺-independent, membrane-potential-sensitive transport mechanism in lobster BBMV. Leucine transport may occur in these membranes by a separate agency.

Key words: lysine transport, brush border membrane vesicles, Na⁺-dependence, membrane potential, ion gradients, Homarus americanus, hepatopancreas

Accepted on July 7, 1986

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