TEA transport by snake renal tubules: choline effects, countertransport, H+-TEA exchange

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Abstract
Tetraethylammonium (TEA) transport by isolated perfused snake (Thamnophis spp.) proximal renal tubules was examined for effects of choline and evidence of countertransport of organic cations and H+-TEA exchange. Choline in perfusate significantly inhibited unidirectional lumen-to-bath flux of TEA and accumulation of labeled TEA by tubule cells, and choline in bath significantly inhibited unidirectional bath-to-lumen flux of TEA and accumulation of labeled TEA by tubule cells. These data indicate that choline inhibits transport of TEA into the cells across both the luminal and peritubular membranes and suggest that it may share the TEA transporter. To examine transport at single membranes in intact tubules, we examined the efflux of labeled TEA across the luminal membrane of tubules covered with oil and across the peritubular membrane of tubules with oil-filled lumens. Unlabeled TEA, choline, and low pH in the perfusate stimulated efflux of labeled TEA across the luminal membrane. These data suggest that TEA transport across the luminal membrane can involve countertransport of organic cations and H+-TEA exchange. Unlabeled TEA, choline, and, to a small extent, low pH in the bath stimulated the efflux of labeled TEA across the peritubular membrane. These data suggest that TEA transport across the peritubular membrane can involve countertransport of organic cations and, possibly, H+-TEA exchange. The efflux data across both membranes further support the idea that choline may share the TEA transporter.