Dual effects of SK&F 96365 in human leukemic HL-60 cells. Inhibition of calcium entry and activation of a novel cation influx pathway.
The effects of the receptor-mediated Ca2+ entry blocker, SK&F 96365 on thapsigargin (TSG)-induced Ca2+ entry in fura-2-loaded HL-60 cells were studied. After Ca2+ release induced by 30 nM TSG, readmission of Ca2+ resulted in a sustained Ca2+ entry, which could be partially inhibited by 1-3 microM SK&F 96365. Surprisingly, SK&F 96365 at 30-100 microM, instead of causing a stronger inhibition, actually promoted Ca2+ entry. Furthermore, at 16-100 microM, this drug released intracellular Ca2+ on its own and induced Ca2+ entry upon readmission of Ca2+. This SK&F 96365-activated Ca2+ entry pathway was insensitive to nifedipine and, interestingly, accessible to Ni2+ and La3+. However, SK&F 96365 (30 microM) almost completely blocked (basal) Mn2+ entry and only caused 4.4% of the cells to be stained with trypan blue, strongly suggesting that the SK&F 96365-activated cation entry was not due to damage nor to a very nonselective permeabilization of the plasma membrane. These data indicate that low concentrations of SK&F 96365 inhibited Ca2+ entry and higher concentrations activated a novel cation entry pathway. Because these 2 opposing effects overlapped at an intermediate concentration (16 microM), which is within the range commonly used to block Ca2+ entry, cautious use of this Ca2+ antagonist appears to be warranted.
Leung
Y M
YM
Department of Physiology, Faculty of Medicine, University of Hong Kong.
Kwan
C Y
CY
Loh
T T
TT
D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D018922:HL-60 Cells; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D007093:Imidazoles; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium