The Journal of General Physiology
Axon Instruments microelectrode amplifiers
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The Journal of General Physiology, Vol 82, 853-874, Copyright © 1983 by The Rockefeller University Press

ARTICLES

Coupling ratio of the Na-K pump in the lobster cardiac ganglion

DR Livengood

The electrogenic Na-K pump coupling ratio in the large neurons of the lobster cardiac ganglion was determined by two different electrophysiological techniques. A graphical analysis plotting exp(EmF/RT) vs. [K]o after the pump was blocked by ouabain was used to determine values for [K]i, PNa/PK, and the pump coupling ratio. These measurements were made 4-8 h after the cells were penetrated with microelectrodes, and thus represent non-Na-loaded steady state values. The value obtained for the pump coupling ratio under these conditions was 1.44 +/- 0.06 (n = 9) or close to 3 Na for 2 K. The second technique used to measure the coupling ratio was to iontophoretically inject Na ions into the neuron. Neurons were penetrated with three microelectrodes, two of which were filled with 2 M Na-citrate; the third electrode contained either 2 M K-citrate or 3 M KCl. By passing current between the Na salt-containing electrodes, Na was injected into the cell soma. The injection system was calibrated by injecting 24Na- citrate into counting vials from representative microelectrodes (calculated 24Na transport = 0.92). By knowing the Na load injected into the cells, and by measuring the time-current area produced by the Na activation of the Na-K pump, the coupling ratio was calculated to be 1.54 +/- 0.05 (n = 19), which is not significantly different from the value obtained by the first method. This value represents a Na-loaded experimental situation. When Na was removed from the external bathing solution, the coupling ratio shifted to 2 Na to 1 K (2.0 +/- 0.07, n = 4). These results suggest that the pump normally operates with a 3:2 ratio both in steady state and under Na load but that in the absence of external Na, it can operate with less than a full complement (2) of K on the external surface of the pump.
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 Biol. Bull.Home page
I. M. Cooke
Reliable, Responsive Pacemaking and Pattern Generation With Minimal Cell Numbers: the Crustacean Cardiac Ganglion
Biol. Bull., April 1, 2002; 202(2): 108 - 136.
[Abstract] [Full Text] [PDF]


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