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Characterization of intracellular pH regulation in the guinea‐pig ventricular myocyte
Author(s) -
Leem Chae Hun,
LagadicGossmann Dominique,
VaughanJones Richard D.
Publication year - 1999
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.1469-7793.1999.0159z.x
Subject(s) - intracellular , intracellular ph , cotransporter , chemistry , biophysics , ion transporter , myocyte , guinea pig , acid–base reaction , base (topology) , biochemistry , sodium , biology , endocrinology , membrane , organic chemistry , mathematical analysis , mathematics
1 Intracellular pH was recorded fluorimetrically by using carboxy‐SNARF‐1, AM‐loaded into superfused ventricular myocytes isolated from guinea‐pig heart. Intracellular acid and base loads were induced experimentally and the changes of pH i used to estimate intracellular buffering power (β). The rate of pH i recovery from acid or base loads was used, in conjunction with the measurements of β, to estimate sarcolemmal transporter fluxes of acid equivalents. A combination of ion substitution and pharmacological inhibitors was used to dissect acid effluxes carried on Na + ‐H + exchange (NHE) and Na + ‐HCO 3 − cotransport (NBC), and acid influxes carried on Cl − ‐HCO 3 − exchange (AE) and Cl − ‐OH − exchange (CHE). 2 The intracellular intrinsic buffering power (β i ), estimated under CO 2 /HCO 3 − ‐free conditions, varied inversely with pH i in a manner consistent with two principal intracellular buffers of differing concentration and p K . In CO 2 /HCO 3 − ‐buffered conditions, intracellular buffering was roughly doubled. The size of the CO 2 ‐dependent component (β CO2 ) was consistent with buffering in a cell fully open to CO 2 . Because the full value of β CO2 develops slowly (2·5 min), it had to be measured under equilibrium conditions. The value of β CO2 increased monotonically with pH i . 3 In 5 % CO 2 /HCO 3 − ‐buffered conditions (pH o 7·40), acid extrusion on NHE and NBC increased as pH i was reduced, with the greater increase occurring through NHE at pH i < 6·90. Acid influx on AE and CHE increased as pH i was raised, with the greater increase occurring through AE at pH i > 7·15. At resting pH i (7·04‐7·07), all four carriers were activated equally, albeit at a low rate (about 0·15 mM min −1 ). 4 The pH i dependence of flux through the transporters, in combination with the pH i and time dependence of intracellular buffering (β i +β CO2 ), was used to predict mathematically the recovery of pH i following an intracellular acid or base load. Under several conditions the mathematical predictions compared well with experimental recordings, suggesting that the model of dual acid influx and acid efflux transporters is sufficient to account for pH i regulation in the cardiac cell. Key properties of the pH i control system are discussed.