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Rapid inhibition of the Na + ‐K + pump affects Na + ‐Ca 2+ exchanger‐mediated relaxation in rabbit ventricular myocytes
Author(s) -
Terracciano C. M. N.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0165b.x
Subject(s) - chemistry , extracellular , diaphragm pump , caffeine , biophysics , sodium , myocyte , barium , calcium , sodium calcium exchanger , endoplasmic reticulum , ion transporter , analytical chemistry (journal) , intracellular , inorganic chemistry , chromatography , biochemistry , endocrinology , materials science , membrane , biology , nanotechnology , organic chemistry , micropump
The direct influence of Na + ‐K + pump activity on the ability of the Na + ‐Ca 2+ exchanger to remove Ca 2+ was investigated in isolated adult rabbit ventricular myocytes. Cell shortening was measured using an edge‐detection system. Cytoplasmic [Ca 2+ ] was monitored using the fluorescent indicator indo‐1. Electrophysiological parameters were recorded using high‐resistance microelectrodes. The Na + ‐K + pump was rapidly inhibited by removal of extracellular K + and measurements were taken almost immediately to minimise effects on other cellular compartments. Activity of the Na + ‐Ca 2+ exchanger was monitored during release of Ca 2+ from the sarcoplasmic reticulum (SR) elicited by rapid application of 15 m m caffeine. When Na + ‐K + pump activity was affected by K + removal, cell relaxation and indo‐1 fluorescence decline were slowed by approximately 40 %. The charge calculated by integrating the caffeine‐induced transient inward current was unchanged, suggesting that there was no difference in the SR Ca 2+ content in the two conditions. However Ca 2+ flux via the Na + ‐Ca 2+ exchanger was slower when the Na + ‐K + pump was inhibited. Similar experiments were performed by inhibiting the Na + ‐K + pump using 0.5 m m strophanthidin. In this condition similar results to the ones observed by K + removal were obtained, suggesting a specific role of the Na + ‐K + pump in the phenomenon observed. This study suggests that the activity of the Na + ‐K + pump influences Na + ‐Ca 2+ exchanger function in the absence of changes in SR Ca 2+ content. This can be explained by a slower removal of Na + from the subsarcolemmal space. The source of the increase in subsarcolemmal [Na + ] requires further investigation. However, calculations derived from modelling suggest that the Na + ‐Ca 2+ exchanger itself could be involved.