Effect of cytoplasmic acidification on the membrane potential of T-lymphocytes: Role of trace metals

Publisher Website
Google Scholar
Abstract
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.