|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 98, 815-833, Copyright © 1991 by The Rockefeller University Press
ARTICLES |
JR Stimers, S Liu and M Lieberman
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710.
The measured apparent affinity (K0.5) of the Na/K pump for ouabain has been reported to vary over a wide range. In a previous report we found that changing Nai could alter apparent affinity by at least an order of magnitude and that the model presented predicted this variability. To increase our understanding of this variability, isolated cells or two- to three-cell clusters of cardiac myocytes from 11-d embryonic chick were used to measure the effects of Nai and Ko on the K0.5 of the Na/K pump for ouabain. Myocytes were whole-cell patch clamped and Na/K pump current (Ip) was measured in preparations exposed to a Ca-free modified Hank's solution (HBSS) that contained 1 mM Ba, 10 mM Cs, and 0.1 mM Cd. Under these conditions there are no Ko-sensitive currents other than Ip because removal of Ko in the presence of ouabain had no effect on the current-voltage (I-V) relation. The I-V relation for Ip showed that in the presence of 5.4 mM Ko and 51 mM Nai, Ip has a slight voltage dependence, decreasing approximately 30% from 0 to -130 mV. Increasing Nai in the patch pipette from 6 to 51 mM (Ko = 5.4 mM) caused Ip to increase from 0.46 +/- 0.07 (n = 5) to 1.34 +/- 0.08 microA/cm2 (n = 13) with a K0.5 for Nai of 17.4 mM and decreased the K0.5 for ouabain from 18.5 +/- 1.8 (n = 4) to 3.1 +/- 0.4 microM (n = 3). Similarly, varying Ko between 0.3 and 10.8 mM (Nai = 24 mM) increased Ip from 0.13 +/- 0.01 (n = 5) to 0.90 +/- 0.05 microA/cm2 (n = 5) with a K0.5 for Ko of 1.94 mM and increased K0.5 for ouabain from 0.56 +/- 0.14 (n = 3-6) to 10.0 +/- 1.1 microM (n = 6). All of these changes are predicted by the model presented. A qualitative explanation of these results is that Nai and Ko interact with the Na/K pump to shift the steady-state distribution of the Na/K pump molecules among the kinetic states. This shift in state distribution alters the probability that the Na/K pump will be in the conformation that binds ouabain with high affinity, thus altering the apparent affinity. In intact cells, the measured apparent affinity represents a combination of all the rate constants in the model and does not equate to simple first-order binding kinetics.(ABSTRACT TRUNCATED AT 400 WORDS)
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  K. S. Richards, K. Bommert, G. Szabo, and R. Miles Differential expression of Na+/K+-ATPase {alpha}-subunits in mouse hippocampal interneurones and pyramidal cells J. Physiol., December 1, 2007; 585(2): 491 - 505. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Krogh-Madsen, P. Schaffer, A. D. Skriver, L. K. Taylor, B. Pelzmann, B. Koidl, and M. R. Guevara An ionic model for rhythmic activity in small clusters of embryonic chick ventricular cells Am J Physiol Heart Circ Physiol, July 1, 2005; 289(1): H398 - H413. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. D. Peluffo, Y. Hara, and J. R. Berlin Quaternary Organic Amines Inhibit Na,K Pump Current in a Voltage-dependent Manner: Direct Evidence of an Extracellular Access Channel in the Na,K-ATPase J. Gen. Physiol., February 23, 2004; 123(3): 249 - 263. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 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]
|
|
|
|
|
|
E. Carmeliet Cardiac Ionic Currents and Acute Ischemia: From Channels to Arrhythmias Physiol Rev, July 1, 1999; 79(3): 917 - 1017. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. T. Liang and J. F. Morley A New Cyclic AMP-independent, Gs-mediated Stimulatory Mechanism via the Adenosine A2a Receptor in the Intact Cardiac Cell J. Biol. Chem., August 2, 1996; 271(31): 18678 - 18685. [Abstract] [Full Text] [PDF]
|
|
|
|
