Na/K pump current in guinea pig cardiac myocytes and the effect of Na leak.
BACKGROUND
Steady-state Na/K pump current (Ip) in adult guinea pig ventricular myocytes was studied to determine the effect on the Na/K pump of transmembrane Na leak, membrane potential, and pipette Na concentration.


RESULTS
Using conventional whole cell, patch clamp techniques, Ip was identified as either Ko-sensitive or ouabain-sensitive current when most other membrane currents were inhibited. Control experiments showed that there were no Ko-sensitive currents other than Ip under the conditions of our experiments. Ip was found to be similar to that reported by others being voltage dependent between -130 and 0 mV and having a half maximal activation by Nai of 28 mM. Ouabain sensitivity was also measured, and it was found that there were two binding sites with the high affinity site comprising 5% to 10% of the total and having an apparent affinity 1000-fold higher than the low affinity site. Apparent affinity of both sites was shifted about 10-fold (higher affinity) by increasing Nai from 10 to 85 mM. When internally perfused with 0 Na solution, Na leak through the membrane was found to be linearly related to Na/K pump activity. In contrast to prior suggestions, Ip was not correlated with series resistance when there was a large transmembrane Na gradient.


CONCLUSIONS
These data suggest that, under conditions of high transmembrane Na gradient, Na leak through the membrane plays a significant role in determining Na/K pump activity.
Dobretsov
M
M
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
Stimers
J R
JR
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D012107:Research Design; D012964:Sodium / Q000494:pharmacology / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*
D000889:Anti-Arrhythmia Agents; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase