Calcium-pH crosstalks in the human mast cell line HMC-1: intracellular alkalinization activates calcium extrusion through the plasma membrane Ca2+-ATPase.
The human mast cell line (HMC-1) has been used to study the relationship between intracellular pH and cytosolic calcium (Ca2+) in mast cells. Thapsigargin (TG) caused store-operated Ca2+ entry, that is enhanced by the PKC activator PMA. NH4Cl-induced alkalinization showed an inhibitory effect on TG-sensitive stores depletion (not on TG-insensitive stores), and also on final cytosolic Ca2+ levels reached in response to both TG and the ionophore ionomycin. Loperamide, a positive modulator of store-operated channels, induced a slight Ca2+ entry by itself, and also increased TG-induced Ca2+ entry. This enhancement was not enough to reverse the inhibitory effect of NH4Cl-induced alkalinization. When comparing the effect of NH4Cl-induced alkalinization on Ca2+ levels, with those observed using Ca2+ channel blockers (namely Ni2+ and SKF-96365), cytosolic profiles for this ion are different, either in modified saline solution or in HCO3(-)-free medium. Thus, it seems unlikely that the inhibitory effect of NH4Cl-induced alkalinization on Ca2+ is taking place by blockage of Ca2+ entry. Furthermore, inhibition of the plasma membrane Ca2+-ATPase (an important mechanism for Ca2+ efflux) with sodium orthovanadate (SO) matches with the inhibition of the negative effect on Ca2+ levels elicited by NH4Cl. Data indicate that NH4Cl-induced alkalinization might be activating Ca2+ efflux from the cell, by stimulation of the plasma membrane Ca2+-ATPase, and also confirm our previous finding that Ca2+ is a secondary signal to activate HMC-1 cells.
Pernas-Sueiras
Octavio
O
Departamento de Farmacología, Facultad de Veterinaria, Universidad Santiago de Compostela, 27002 Lugo, Spain.
Alfonso
Amparo
A
Vieytes
Mercedes R
MR
Orfao
Alberto
A
Escribano
Luis
L
Francisca
Sánchez-Jiménez
SJ
Botana
Luis M
LM
D000643:Ammonium Chloride / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000378:metabolism; D008407:Mast Cells / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000378:metabolism; D019284:Thapsigargin / Q000378:metabolism
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007093:Imidazoles; D000643:Ammonium Chloride; D019284:Thapsigargin; D009532:Nickel; D000252:Calcium-Transporting ATPases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium