Ca2+ release and Ca2+ entry induced by rapid cytosolic alkalinization in Jurkat T-lymphocytes.
4-Aminopyridine (4-AP), a compound usually known as a K(+)-channel inhibitor, induced rapid cytosolic alkalinization from pH 7.15 to pH 7.4, and subsequently Ca2+ mobilization in the T-lymphocyte cell line Jurkat. Other weak bases, such as NH4Cl or triethanolamine, induced a smaller and/or slower increase in cytosolic pH, resulting in a lower or no detectable Ca2+ signal. In the presence of extracellular Ca2+, 4-AP mediated a rapid and sustained increase in the free cytosolic Ca2+ concentration similar to that obtained by T-cell receptor-mediated stimulation. In the absence of extracellular Ca2+, 4-AP transiently released Ca2+ from an intracellular store that is most likely identical with the agonist- and Ins(1,4,5)P3-sensitive Ca2+ pool of Jurkat T-cells. As possible mechanisms for Ca2+ release from this particular pool as induced by 4-AP we examined (i) formation of Ins(1,4,5)P3 and (ii) sensitization of the Ins(1,4,5)P3-receptor/Ca(2+)release system by increasing intracellular pH. Although 4-AP did not induce formation of inositol polyphosphates, as demonstrated by h.p.l.c. analysis, in permeabilized cells the dose-response curve for Ins(1,4,5)P3 was shifted to the left by changing the intracellular pH from 7.2 to 7.4. This indicated that sensitization of the Ins(1,4,5)P3-receptor/Ca(2+)-release system was responsible for the effects of 4-AP seen in intact cells. In conclusion, 4-AP appears a novel tool for depletion of the agonist-sensitive Ca2+ pool of T-cells without simultaneous formation of Ins(1,4,5)P3, thereby inducing capacitative Ca2+ entry in these cells.
Max-Planck-Society, Clinical Research Unit for Rheumatology/Immunology, University Erlangen-Nürnberg, Germany.
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Guse
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Roth
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Emmrich
D015761:4-Aminopyridine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D015544:Inositol 1,4,5-Trisphosphate; D015761:4-Aminopyridine; D002118:Calcium