Crosstalk between cytosolic pH and intracellular calcium in human lymphocytes - Effect of 4-aminopyridin, ammonium chloride and ionomycin

Stimulation of lymphocytes by specific antigens is followed by the activati on of different signal transduction mechanisms, such as alterations in the cytoplasmic levels of Ca2+, H+ and variations in membrane potential. To stu dy interrelationships among these parameters, changes in pHi and Ca2+ were measured with the fluorescent probes BCECF and Fura-2 in freshly isolated b lood human lymphocytes. Moreover, membrane potential qualitative alteration s were recorded with the fluorescent dye bisoxonol. In a bicarbonate-free m edium, cell alkalinization with NH4Cl slightly decreased intracellular Ca2 concentration ([Ca2+](i)) due to efflux of Ca2+ from the cell. In contrast , an elevation of pHi induced with 4-AP increased [Ca2+](i), either in the presence or absence of external Ca2+. The increase in Ca2+-free medium is l ikely to be due to Ca2+ release from thapsigargin and caffeine-independent intracellular stores. Both 4-AP or NH4Cl induced a plasma membrane depolari sation, although with different kinetics. The ionosphere ionomycin increase d pHi, Ca2+ levels and also induced membrane depolarisation. Together, thes e observations demonstrate a lack of correlation between the magnitude of c hanges in pHi and Ca2+. (C) 2000 Elsevier Science Inc. All rights reserved.