Effect of cytoplasmic acidification on the membrane potential of T-lymphocytes: Role of trace metals |
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Authors: | Michael J Mason Sergio Grinstein |
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Institution: | (1) Division of Cell Biology, Hospital for Sick Children, M5G 1X8 Toronto, Ontario, Canada;(2) Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada |
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Abstract: | Summary The effect of lowering intracellular pH on the membrane potential (E
m
) of rat thymic lymphocytes was studied using the potential-sensitive dyebis-oxonol. Cells were acid loaded by addition of the electroneutral K+/H+ exchanging ionophore nigericin. Acidification to pH 6.3 in Na+-free solution resulted in a biphasic change inE
m
: an early transient hyperpolarization followed by a sustained depolarization. These changes were associated with a rise in cytosolic free Ca2+ (Ca2+]
i
). The hyperpolarization was eliminated when the change in Ca2+]
i
was prevented using BAPTA, an intracellular Ca2+ chelator. Moreover, a similar hyperpolarization was elicited by elevation of Ca2+]
i
at physiological pH
i
using ionomycin, suggesting involvement of Ca2+-activated K+ channels. In contrast, the depolarization phase could not be mimicked by raising Ca2+]
i
with ionomycin. However, intracellular BAPTA effectively inhibited the acidificationinduced depolarization. Inhibition was also obtained by extracellular addition of EGTA or dithiothreitol, even when the external free Ca2+ concentration remained unaltered. These observations suggested a possible role of contaminating trace metals. Cytosolic acidification is envisaged to induce intracellular accumulation of one or more trace metals, which induces the observed changes inE
m
. Accordingly, similar changes inE
m
can be induced without acidification by the addition of small amounts of Cu2+ to the medium. The ionic basis of theE
m
changes induced by acidification and the significance of these observations are discussed. |
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Keywords: | intracellular pH cytoplasmic Ca2+ thymic lymphocytes chelator trace metals nigericin |
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