ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The effects of various agents on active sodium transport were studied in the toad bladder in terms of the equivalent circuit comprising an active conductanceK a, an electromotive forceE Na, and a parallel passive conductanceK p. For agents which affectK a, but notE Na orK p, the inverse slope of the plot of total conductance κ against short-circuit currentI 0 evaluatesE Na, and the intercept representsK p. Studies employing 5×10−7 m amiloride to depressK a indicate a changingE Na, invalidating the use of the slope technique with this agent. An alternative suitable technique employs 10−5 m amiloride, which reducesI 0 reversibly to near zero without effect onK p. Despite curvilinearity of the κ-I0 plot under these conditions,K p may therefore be estimated fairly precisely from the residual conductance. It then becomes possible to follow the dynamic behavior ofK a andE Na (in the absence of 10−5 m amiloride) by frequent measurements of κ andI 0, utilizing the relationshipsK a=K-K p, andK Na=I O/(K-K p). 2-deoxy-d-glucose (7.5×10−3 m) depressedK a without affectingE Na. Amiloride (5×10−7 m) depressedK a and enhancedE Na. Vasopressin (100 mU/ml) enhancedK a markedly and depressedE Na slightly. Ouabain (10−4 m) depressed bothK a andE Na. All of the above effects were noted promptly;K p was unaffected. The “electromotive force of Na transport”E Na appears not to be a pure energetic parameter, but to reflect kinetic factors as well, in accordance with thermodynamic considerations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01869693
Permalink
