Sodium cyanide increases cytosolic free calcium: evidence for activation of the reversed mode of the Na+/Ca2+ exchanger and Ca2+ mobilization from inositol trisphosphate-insensitive pools.
This study characterized the cytosolic free Ca2+ concentration ([Ca2+]i) in NaCN-treated human A-431 cells. The resting [Ca2+]i was 85 +/- 8 nM (n = 141) in untreated cells at 37 degrees C, determined with the fura-2 fluorescence probe. When cells were treated with NaCN, [Ca2+]i increased in a time- and NaCN concentration-dependent manner. When cells were exposed to 10 mM NaCN for 10 min, [Ca2+]i increased 278 +/- 28% (n = 5) but returned to normal within 45 min after treatment. The [Ca2+]i increase depended on the presence of external Ca2+. La3+ and Cd2+, but not verapamil or nifedipine, inhibited the NaCN-induced [Ca2+]i increase. The NaCN-induced [Ca2+]i increase also depended on external Na+ (K1/2 = 85 mM). The intracellular Na+ concentration, measured with the fluorescence probe SBFI, increased 267 +/- 16% after NaCN treatment. The NaCN-induced [Ca2+]i increase was modulated by treatment with ouabain or veratridine and was completely blocked by tetrodotoxin, amiloride (K1/2 = 5.4 microM), and dichlorobenzamil (K1/2 = 0.28 microM). These results suggest NaCN activates the Na+/Ca2+ exchange system. TMB-8 and ryanodine both partially blocked the increase in [Ca2+]i in the presence of external Ca2+, indicating that Ca2+ release from intracellular pools also occurred after the initial Ca2+ influx. NaCN decreased inositol trisphosphates production. U-73122, bradykinin, or monensin did not prevent the NaCN-induced increase in [Ca2+]i. However, the magnitude of the [Ca2+]i increase caused by NaCN was abolished in ionomycin-treated the [Ca2+]i increase caused by NaCN was abolished in ionomycin-treated cells, indicating that intracellular Ca2+ release induced by NaCN is derived from an ionomycin-sensitive Ca2+ pool. The results suggest that NaCN initially increased Na+ influx, which activated the reverse mode of a Na+/Ca2+ exchanger, leading to an increase in Ca2+ influx. The Ca2+ influx induced a Ca2+ mobilization from only an ionomycin-sensitive intracellular Ca2+ pool containing ryanodine receptors.
Kiang
J G
JG
Department of Clinical Physiology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
Smallridge
R C
RC
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D002352:Carrier Proteins / Q000187:drug effects* / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D008985:Monensin / Q000494:pharmacology; D009124:Muscle Proteins / Q000187:drug effects / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D012966:Sodium Cyanide / Q000494:pharmacology*; D019831:Sodium-Calcium Exchanger; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D002352:Carrier Proteins; D007295:Inositol Phosphates; D007473:Ion Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; C041470:3',4'-dichlorobenzamil; D012433:Ryanodine; D015759:Ionomycin; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D012966:Sodium Cyanide; D001920:Bradykinin; D002118:Calcium