Premium
Bicarbonate abolishes intracellular alkalinization in mitogen‐stimulated 3T3 cells
Author(s) -
Szwergold Benjamin S.,
Brown Truman R.,
Freed Jerome J.
Publication year - 1989
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.1041380203
Subject(s) - bicarbonate , intracellular ph , intracellular , chemistry , biochemistry , biophysics , stimulation , biology , endocrinology , organic chemistry
An increase in intracellular pH (pH i ) following mitogenic stimulation has been reported in a variety of mammalian cells ( W. Moolenaar, Annu. Rev. Physiol. , 48:363–376, 1986; E. Rozengurt, Science , 234:161–166, 1986). This increase is currently believed to constitute a “permissive” signal in the process of cell activation (A.E. Lagarde and J.M. Pouyssegur, Cancer Biochem. Biophys. 9: 1–14, 1986). Since the majority of studies of this phenomenon have been conducted in the nonphysiological milieu of bicarbonate‐free solutions, we have undertaken a study of the effects of bicarbonate and CO 2 on mitogen‐induced intracellular alkalinization in NIH 3T3 cells. Using nuclear magnetic resonance (NMR) spectroscopy and novel 31 P NMR pH indicators (2‐amino‐phosphono‐carboxylic acids) we found that mitogen induces an increase in pH i of 0.16 units only in cells bathed in medium containing low concentrations of bicarbonate (less than 1 mM) and not in cells bathed in medium containing physiological levels of bicarbonate (10–30 mM). In addition to abolishing the mitogen‐induced alkalinization, bicarbonate stabilizes pH i at 7.25 units as the external pH (pH e ) is varied from 7.0 to 7.6. In contrast, in a bicarbonate‐free medium pH i increases from 6.9 to 7.3 over the same range of external pHs. At a constant external pH, increasing the bicarbonate/CO 2 concentration results in an increase in pH i from 6.9 in bicarbonate‐free solution to 7.25 in a bicarbonate‐buffered medium. This relationship is hyperbolic with half‐maximal effect occurring at a concentration of 0.4 mM bicarbonate at pH 7.05 and 37°C. Our results suggest that the observations of mitogen‐induced alkalinization may be due to the use of nonphysiological bicarbonate‐free media. Since this increase in pH i is not observed in physiological media where bicarbonate concentrations are usually greater than 20 mM, we conclude that an increase in pH i is not an obligatory or usual part of the cellular response to growth factors in vivo.