ISSN:
1432-1424
Keywords:
sodium transport
;
electrophysiology
;
urinary bladder
;
current-voltage relations
;
epithelial transport
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The “instantaneous” transepithelial current-voltage (I–V) relations ofNecturus urinary bladder were determined under short-circuit conditions during impalement of a cell with a microelectrode as described previously (Thompson et al.,J. Membrane Biol. 66: 41–54, 1982). These studies were performed in the presence of 5, 15 and 45mm Na in the mucosal solution, [Na] m , and in the absence and presence of a maximally effective dose of amiloride. TheI–V relations of the amiloride-sensitive Na-entry step at the apical membrane conformed closely to that predicted by the Goldman-Hodgkin-Katz (GHK) “constant field” flux equation over a wide range under all conditions. From theseI–V relations we calculated: (a) the permeability of the apical membrane to Na,P Na m ; (b) thechord conductance of the apical membrane to Na under short-circuit conditions,0 G Na m ; and, (c) the intracellular Naactivity, (Na) c . In addition, from theI–V relations in the absence and presence of amiloride and the voltage-divider ratio, we determined theslope conductances of the transcellular pathway (g c) and the apical (g m) and basolateral (g s) membranes at each different steady state. Our findings indicate that: (a) While the rate of active Na transport (I sc) increases hyperbolically with increasing [Na] m , (Na) c is maintained constant at approximately 6mm and is independent of both [Na] m and theI sc. (b) The increase inI sc with increasing [Na] m is entirely attributable to an increase in0 G Na m ; the thermodynamic driving force for Na-entry across the apical membrane is maintained constant under these conditions. (c) P Na m decreases with increasing [Na] m . (d) g c, gm andg s increase linearly with increasingI sc. A possible mechanism that could account forboth the increase in basolateral pump activity in the face of a constant (Na) c ,and the increase ing s that parallels the increase in pump activity is the “recruitment” of additional “pump-leak units” to the basolateral membrane with increasing [Na] m . Other possibilities are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870439
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