Dual effects of tetrandrine on cytosolic calcium in human leukaemic HL-60 cells: intracellular calcium release and calcium entry blockade.
1. Tetrandrine (TET, a Ca2+ antagonist of Chinese herbal origin) and thapsigargin (TSG, an endoplasmic reticulum Ca2+ pump inhibitor) concentration-dependently mobilized Ca2+ from intracellular stores of HL-60 cells, with EC50 values of 20 microM and 0.8 nM, respectively. After intracellular Ca2+ release by 30 nM TSG, there was no more discharge of Ca2+ by TET (100 microM), and vice versa. 2. Pretreatments with 100 nM rauwolscine (alpha 2-adrenoceptor antagonist), 100 nM prazosin (alpha 1-adrenoceptor antagonist), 10 nM phorbol myristate acetate (PMA, a protein kinase C activator) or 100 nM staurosporine (a protein kinase C inhibitor) had no effect on 100 microM TET-induced intracellular Ca2+ release. 3. After intracellular Ca2+ release by 30 nM TSG in Ca(2+)-free medium, readmission of Ca2+ caused a substantial and sustained extracellular Ca2+ entry. The latter was almost completely inhibited by 100 microM TET (IC50 of 20 microM) added just before Ca2+ readmission. In Ca(2+)-containing medium, 30 nM TSG caused a sustained phase of cytosolic Ca2+ elevation, which could be abolished by 100 microM TET. TET was also demonstrated to retard basal entry of extracellular Mn2+ and completely inhibit TSG-stimulated extracellular Mn2+ entry. 4. TSG-induced extracellular Ca2+ entry was insensitive to the L-type Ca2+ channel blocker, nifedipine (1 microM), but was completely inhibited by the non-selective Ca2+ channel blocker La3+ (300 microM). Depolarization with 100 mM KCl did not raise the cytosolic Ca2+ level. 5. These data suggest that (a) TET and TSG mobilized the same Ca2+ pool and TET-induced intracellular Ca2+ release was independent of protein kinase C activity and ox-adrenoceptor activation,and (b) TET blocked the voltage-insensitive Ca2+ entry pathway activated by TSG. These dual effects on HL-60 cells were also observed with hernandezine (HER), a TET-like compound and in another cell type, murine B lymphoma M12.4 cells.
Department of Physiology, Faculty of Medicine, University of Hong Kong.
Y M
YM
Leung
C Y
CY
Kwan
T T
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Loh
D000470:Alkaloids / Q000494:pharmacology*; D044182:Benzylisoquinolines; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism / Q000473:pathology; D009543:Nifedipine / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D011942:Receptors, Adrenergic, alpha; D013729:Terpenes; C009438:tetrandrine; C067193:hernandezine; D019284:Thapsigargin; D011493:Protein Kinase C; D009543:Nifedipine; D002118:Calcium