Beta-chemokines and human immunodeficiency virus type-1 proteins evoke intracellular calcium increases in human microglia.
Activation of beta-chemokine receptors, co-receptors for human immunodeficiency virus type-1 (HIV-1), stimulates movement and secretion in microglia, possibly through a Ca(2+)-dependent mechanism. We studied chemokine activation of Ca(2+) signaling processes in microglia. Human fetal microglia were grown in primary culture and chemokine-induced increases in intracellular calcium concentration ([Ca(2+)](i)) were measured in single cells using indo-1-based microfluorimetry. Application of 50 ng/ml regulated on activation, normal T expressed and secreted (RANTES; 120 s) evoked responses in 26% of the microglia (187/719 cells). [Ca(2+)](i) increased from a basal level of 66+/-6 nM to peak at 268+/-23 nM (n=187). Chemokine-evoked responses rapidly desensitized as indicated by the rapid return to basal [Ca(2+)](i) levels in the maintained presence of RANTES. The removal of extracellular Ca(2+) or stimulation in the presence of Ni(2+) (2mM) or La(3+) (100 microM) blocked the RANTES-elicited [Ca(2+)](i) increase. The L-type calcium channel antagonist nimodipine (10 microM) inhibited the RANTES-mediated increase in [Ca(2+)](i) by 80+/-16%. Thus, the RANTES-evoked calcium transient appears to result from Ca(2+) influx with little if any release from intracellular stores. Application of gp120(clade) (E) and gp120(CM235) (50 ng/ml) neither mimicked nor antagonized the RANTES-evoked response. Application of 50 ng/ml eotaxin (120 s) evoked an increase in [Ca(2+)](i) in 13% of the human microglia in culture (61/469 cells). The HIV-1 regulatory protein Tat (50 ng/ml) increased the [Ca(2+)](i) in a subset of eotaxin-responsive cells (16/30). The L-type calcium channel antagonist nimodipine (3 microM) inhibited eotaxin- and Tat-mediated increases in [Ca(2+)](i) by 88+/-6% and 93+/-6%, respectively. Thus, activation of CCR3 appears to evoke Ca(2+) influx through L-type Ca(2+) channels.These results indicate that beta-chemokines, RANTES and eotaxin, activate a nimodipine sensitive Ca(2+) influx pathway in human fetal microglia. HIV-1 Tat protein mimicked chemokine-mediated Ca(2+) signaling and may modulate the migratory and secretory responses of microglia.
Hegg
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Department of Pharmacology, University of Minnesota, Minneapolis, MN 55455, USA.
Hu
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Peterson
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Thayer
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D000163:Acquired Immunodeficiency Syndrome / Q000276:immunology / Q000378:metabolism; D001921:Brain / Q000166:cytology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D054413:Chemokine CCL11; D018946:Chemokine CCL5 / Q000494:pharmacology; D019742:Chemokines, CC / Q000494:pharmacology*; D016207:Cytokines / Q000494:pharmacology; D005333:Fetus / Q000166:cytology; D015696:Gene Products, tat / Q000494:pharmacology; D015699:HIV Envelope Protein gp120 / Q000494:pharmacology*; D006801:Humans; D017628:Microglia / Q000166:cytology / Q000378:metabolism* / Q000821:virology*; D009553:Nimodipine / Q000494:pharmacology; D054322:tat Gene Products, Human Immunodeficiency Virus
C515456:CCL11 protein, human; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D054413:Chemokine CCL11; D018946:Chemokine CCL5; D019742:Chemokines, CC; D016207:Cytokines; D015696:Gene Products, tat; D015699:HIV Envelope Protein gp120; D054322:tat Gene Products, Human Immunodeficiency Virus; D009553:Nimodipine; D002118:Calcium