| Abstract: | Basolateral membranes purified from rat jejunal enterocytes and enriched 14 times in (Na, K)-ATPase, are present as unsealed and right side out (RSO) or inside out (IO) vesicles in the ratio 2:2:1, as determined by detergent activation of ATPase activity. Entrance of 1 mM Na into basolateral membrane vesicles was measured in the presence and in the absence of 5 mM ATP by a rapid filtration technique, under different experimental conditions. Carrier-mediated Na transport across the basolateral membrane can be trans-stimulated and cis-inhibited by K and further stimulated by ATP (activation of the Na pump). The ATP effect can be suppressed by vanadate and strophanthidin and enhanced by bleomycin (19% increase), which positively also acts on (Na, K)-ATPase activity (16% increase). In addition to the Na pump this study demonstrates the existence of a carrier-mediated Na transport trans-stimulated by K. There appears to be no cotransport of Na-K. |
