Crosstalk between cytosolic pH and intracellular calcium in human lymphocytes: effect of 4-aminopyridin, ammoniun chloride and ionomycin.
Stimulation of lymphocytes by specific antigens is followed by the activation of different signal transduction mechanisms, such as alterations in the cytoplasmic levels of Ca(2+), H(+) and variations in membrane potential. To study interrelationships among these parameters, changes in pHi and Ca(2+) were measured with the fluorescent probes BCECF and Fura-2 in freshly isolated blood human lymphocytes. Moreover, membrane potential qualitative alterations were recorded with the fluorescent dye bis-oxonol. In a bicarbonate-free medium, cell alkalinization with NH(4)Cl slightly decreased intracellular Ca(2+) concentration ([Ca(2+)](i)) due to efflux of Ca(2+) from the cell. In contrast, an elevation of pHi induced with 4-AP increased [Ca(2+)](i), either in the presence or absence of external Ca(2+). The increase in Ca(2+)-free medium is likely to be due to Ca(2+) release from thapsigargin and caffeine-independent intracellular stores. Both 4-AP or NH(4)Cl induced a plasma membrane depolarisation, although with different kinetics. The ionosphere ionomycin increased pHi, Ca(2+) levels and also induced membrane depolarisation. Together, these observations demonstrate a lack of correlation between the magnitude of changes in pHi and Ca(2+).
Cabado
A G
AG
Departamento de Fisiología, E-27002, Universidad Santiago de Compostela, Lugo, Spain.
Alfonso
A
A
Vieytes
M R
MR
González
M
M
Botana
M A
MA
Botana
L M
LM
D015761:4-Aminopyridine / Q000494:pharmacology*; D000643:Ammonium Chloride / Q000494:pharmacology*; D020013:Calcium Signaling / Q000187:drug effects*; D003600:Cytosol / Q000378:metabolism*; D005452:Fluoresceins / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D008214:Lymphocytes / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D026902:Potassium Channel Blockers
D005452:Fluoresceins; D005456:Fluorescent Dyes; D007476:Ionophores; D026902:Potassium Channel Blockers; D000643:Ammonium Chloride; D015759:Ionomycin; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D015761:4-Aminopyridine; D016257:Fura-2