AJP - Cell Physiology, Vol 259, Issue 5 C727-C737, Copyright © 1990 by American Physiological Society
Heat induces intracellular acidification in human A-431 cells: role of Na(+)-H+ exchange and metabolism
J. G. Kiang, L. C. McKinney and E. K. Gallin
Department of Physiology, Armed Forces Radiobiology Research Institute, Bethesda, Maryland 20814-5145.
The resting intracellular pH (pHi) of A-431 cells at 37 degrees C in Na+
Hanks' solution is 7.23 +/- 0.02. In the presence of amiloride (100 microM)
pHi decreases to 7.08 +/- 0.03. Hyperthermia induces a temperature- and
time-dependent intracellular acidification of 0.2 pH units in either
bicarbonate-free or bicarbonate-buffered solutions. After heat treatment
(45 degrees C, 10 min) pHi returns to normal 1 h after incubation at 37
degrees C. The activity of the Na(+)-H+ exchanger was examined in heated
and unheated cells in the absence of bicarbonate. Unheated cells recover
from an acid load in a [Na+]o-dependent and amiloride-sensitive manner. The
apparent Michaelis constant for extracellular Na+ is 38 +/- 9 mM, and the
apparent mean affinity constant for amiloride is 11 +/- 3 microM. In heated
cells the apparent affinity of the Na(+)-H+ exchanger for extracellular Na+
is not changed, but the maximal recovery rate is approximately 40% slower
than that of unheated cells. The rate of recovery from acid loading returns
to normal 2 h after heat treatment. [Na+]i and intrinsic buffering power in
heated cells are the same as those in unheated cells. Decreases in both
intracellular ATP and lactic acid are observed in heated cells.
2-Deoxy-D-glucose and sodium azide induce an intracellular acidification
but prevent most of the acidification induced by heat. Heat treatment
causes no further acidification in cells that are acidified by both
amiloride and 2-deoxy-D-glucose together. These data are the first to
suggest that thermally induced intracellular acidification is due to both
an inhibition of Na(+)-H+ exchange and an inhibition of metabolic pathways.
