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Modulation of Ca 2+ ‐mediated K + ‐gating of erythrocyte ghosts by external Ca‐EGTA
Author(s) -
Benjamin A. M.,
Quastel D. M. J.
Publication year - 1984
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041210309
Subject(s) - egta , chemistry , biophysics , calcium , ionophore , membrane , chromatography , analytical chemistry (journal) , biochemistry , biology , organic chemistry
Using 86 RB + as a marker for K + permeability, we find that extracellular Ca‐EGTA influences the rate of 86 Rb + efflux from erythrocyte ghosts preloaded with 86 Rb + and “buffered” Ca 2+ . At an internal free Ca 2+ , where the rate of 86 Rb + efflux is minimal and uninfluenced by either external EGTA or external Ca 2+ , external Ca‐EGTA at 0.2–0.5 mM can raise the flux rate to as high as can be attained by raising internal Ca 2+ , in the presence of an excess externally either of Ca 2+ or of EGTA. Higher concentrations of Ca‐EGTA (up to 1–2 mM) diminish the flux rate. External Ca‐EDTA or Mg‐EDTA can substitute for Ca‐EGTA in enhancing and suppressing flux rate. The peak rate is insensitive to external free Ca 2+ but depends on internal Ca 2+ ; internal Mg‐EDTA does not substitute for internal Ca‐EGTA. Thus, the erythrocyte membrane is asymmetric with respect to its interaction with Ca 2+ and Ca‐EGTA. Also, 22 Na + does not substitute for 86 Rb + . The peak rate of 86 Rb + flux produced by external Ca‐EGTA is diminished by chlorpromazine (0.1 mM) and augmented by 1‐propranolol (25 μM), in the same way as the rate produced by increasing internal Ca 2+ . The results suggest that external Ca‐EGTA enhances the affinity of internal Ca 2+ for its receptor(s) which operate the K + ‐gate at the inner surface of the membrane. At external concentrations of Ca‐EGTA above 1–2 mM, 86 Rb + flux rate again rises with increase of Ca‐EGTA. This phenomenon does not depend upon internal Ca 2+ , is not affected by chlorpromazine or by 1‐propranolol, and is associated with an enhanced permeability to 22 Na + , inulin, and haemoglobin.