title: Dependence of intracellular Na+ concentration on apical and basolateral membrane Na+ influx in frog skin.
abstract: An isotopic method was developed to measure the intracellular Na+ content of the transepithelial Na+ transport pool of frog skin. Isolated epithelia (no corium) were labeled with 24Na either asymmetrically, from apical (Aa) or basolateral (Ab) solutions, or symmetrically (Aab). Transport pool Na+ could be identified from the kinetics of washout of 24Na carried out in the presence of 1 mM ouabain, 100 microM amiloride, and 1 mM furosemide that served to trap cold Na+ and 24Na within the transport pool. In control epithelia, Aab averaged 64.1 neq/cm2 (13.9 mM), and maximal inhibition of apical membrane Na+ entry with 100 microM amiloride caused Aab to decrease to 24.3 neq/cm2 (5.3 mM). Ouabain caused Aab to increase markedly to 303 neq/cm2 in 30 min, whereas amiloride inhibition of apical membrane Na+ entry reduced markedly the rate of increase of Aab caused by ouabain (7.3 neq X cm-2 X min-1 in control and 1.7 neq X cm-2 X min-1 in the presence of amiloride). These data, in part, confirmed the existence of an important basolateral membrane permeability to Na+ that was measured in separate studies of the bidirectional 24Na fluxes at the basolateral membranes of the cells. Both sets of data were supportive of the idea that a significant Na+ recycling exists at the basolateral membranes of the cells that contributes to the Na+ load on the pump and Na+ recycling participates in the regulation of the Na+ concentration of the Na+ transport pool of these epithelial cells.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D004848:Epithelium / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D011894:Rana pipiens; D012867:Skin / Q000378:metabolism*; D012879:Skin Physiological Phenomena; D012964:Sodium / Q000378:metabolism*; D012979:Sodium Radioisotopes
chemical_list: D012979:Sodium Radioisotopes; D010042:Ouabain; D000584:Amiloride; D005665:Furosemide; D012964:Sodium