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Interaction of the Na + ‐K + pump and Na + ‐Ca 2+ exchange via [Na + ] i in a restricted space of guinea‐pig ventricular cells
Author(s) -
Fujioka Yasutada,
Matsuoka Satoshi,
Ban Toshihiko,
Noma Akinori
Publication year - 1998
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.1469-7793.1998.457bn.x
Subject(s) - chemistry , sarcolemma , isotopes of calcium , egta , analytical chemistry (journal) , calcium , membrane , chromatography , biochemistry , organic chemistry
1 The whole‐cell Na + ‐K + pump current ( I Na‐K ) and Na + ‐Ca 2+ exchange current ( I Na‐Ca ) were recorded in guinea‐pig ventricular myocytes to study the interaction between the two Na + transport mechanisms. 2 INa‐K was isolated as an external K + ‐induced current, and I Na‐Ca as an external Ca 2+ ‐ induced or Ni 2+ ‐sensitive current. The experimental protocol used for one ion carrier did not affect the other. 3 The amplitude of I Na‐K decreased to 54 ± 17 % of the initial peak during continuous application of K + with 20 mM Na + in the pipette. The outward I Na‐Ca , which was intermittently activated by brief applications of Ca 2+ , decreased during activation of I Na‐K , and recovered after cessation of I Na‐K activation. These findings revealed a dynamic interaction between I Na‐K and I Na‐Ca via a depletion of Na + under the sarcolemma. 4 To estimate changes in Na + concentration ([Na + ] i ) under the sarcolemma, the reversal potential (V rev ) of I Na‐Ca was measured. Unexpectedly, V rev hardly changed during activation of I Na‐K . However, when I Na‐Ca was blocked by Ni 2+ at the same time that I Na‐K was activated, V rev changed markedly, maximally by +100 mV, immediately after the removal of Ni 2+ and K + . 5 Subsarcolemmal [Na + ] i was calculated from the V rev of I Na‐Ca on the assumption that the subsarcolemmal Ca 2+ concentration ([Ca 2+ ] i ) was fixed with EGTA, and mean [Na + ] i was calculated from both the time integral of I Na‐K and the cell volume. The subsarcolemmal [Na + ] i was about seven times greater than the mean [Na + ] i . 6 The interaction between the Na + ‐K + pump and Na + ‐Ca 2+ exchange was well simulated by a diffusion model, in which Na + diffusion was restricted to one‐seventh (14 %) of the total cell volume.