HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Daut, J. Articles by Rüdel, R. Search for Related Content PubMed PubMed Citation Articles by Daut, J. Articles by Rüdel, R.

Physiologisches Institut der Technischen Universität München, Biedersteiner Strasse 29, 8000 München 40, Federal Republic of Germany

1. The inhibition of the electrogenic sodium pump in guinea-pig ventricular muscle by cardiac glycosides was studied with a voltage-clamp technique.

2. Superfusion of the preparation with dihydro-ouabain (DHO) produced a reversible depolarization of up to 7 mV. When the membrane potential was clamped to a constant value near the resting potential application of DHO produced a corresponding current change in the inward direction which reached a steady state in less than 1 min.

3. The drug-induced current change (I_D) was found to be the result of a parallel shift of the current—voltage relation. The contributions of a change in extracellular K or intracellular Na to the measured I_D were shown to be very small. From these findings and the results summarized below it was concluded that I_D represents the blockage of the electrogenic pump current by DHO and that it is proportional to the number of drug molecules bound to the Na—K-ATPase in the intact cell.

4. The dependence of I_D on the concentration of DHO applied (5 x 10^-6-8 x 10^-4 M) was found to be consistent with the predictions of the law of mass action for reversible one-to-one binding of the drug to the Na—K pump under equilibrium conditions. From a Scatchard-type plot the equilibrium dissociation constant (K_D) of DHO was determined to be 4·6 (±2·3) x 10^-5 M.

5. The steady-state pump current in the resting preparation was calculated to be 0·81±0·26 µA/cm². It contributed 6·4±0·9 mV to the resting potential in Tyrode solution containing 3 mM-K.

6. In the smallest preparations used the measured time course of the onset and decay of I_D agreed with the chemical kinetics of binding and unbinding calculated for various DHO concentrations. The rate constant of unbinding (k₂) was found to be 3·4 (±0·7) x 10^-2 S^-1 and the average rate constant of binding (k₁) was 7·4 x 10² M^-1 S^-1.

7. By comparing the effects of ouabain and DHO in the same preparation the following estimates of the chemical constants of ouabain binding to the Na—K pump were obtained: K_D 1·5 x 10^-6 M; k₁ 4 x 10³ M^-1 S^-1; k₂ 6 x 10^-3 S^-1.

8. An analysis of the transmembrane movements of Na and K in the steady state showed that the measured pump current density is consistent with a counter-transport of 3 Na and 2 K ions.

This article has been cited by other articles:

				H. G. Glitsch Electrophysiology of the Sodium-Potassium-ATPase in Cardiac Cells Physiol Rev, October 1, 2001; 81(4): 1791 - 1826. [Abstract] [Full Text] [PDF]

				K. Quinn, C. Guibert, and D. J. Beech Sodium-potassium-ATPase electrogenicity in cerebral precapillary arterioles Am J Physiol Heart Circ Physiol, July 1, 2000; 279(1): H351 - H360. [Abstract] [Full Text] [PDF]