Regulation of cytoplasmic calcium levels by two nitric oxide receptors.
We examined the effects of dissolved nitric oxide (NO) gas on cytoplasmic calcium levels ([Ca(2+)](i)) in C6 glioma cells under anoxic conditions. The maximum elevation (27 +/- 3 nM) of [Ca(2+)](i) was reached at 10 microM NO. A second application of NO was ineffective if the first was >0.5 microM. The NO donor diethylamine/NO mimicked the effects of NO. Acute exposure of the cells to low calcium levels was without effect on the NO-evoked response. Thapsigargin (TG) increased [Ca(2+)](i) and was less effective if cells were pretreated with NO. Hemoglobin inhibited the effects of NO at a molar ratio of 10:1. 8-Bromo-cGMP was without effect on the NO-evoked response. If cells were pretreated with TG or exposed chronically to nominal amounts of calcium, NO decreased [Ca(2+)](i). The results suggest that C6 glioma cells have two receptors for NO. One receptor (NO(A)) elevates [Ca(2+)](i) and resides on the endoplasmic reticulum (ER). The other receptor (NO(B)) decreases [Ca(2+)](i) and resides on the plasmalemma or the ER. The latter receptor dominates when the level of calcium within intracellular stores is diminished.
Bowman
C L
CL
Buffalo Institute for Medical Research, Veterans Administration Medical Center, Buffalo, New York 14215-1129, USA. bowman@acsu.buffalo.edu
Yohe
L
L
Lohr
J W
JW
D000332:Aerobiosis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005910:Glioma; D006454:Hemoglobins / Q000494:pharmacology; D006706:Homeostasis; D006834:Hydrazines / Q000494:pharmacology; D007700:Kinetics; D009569:Nitric Oxide / Q000494:pharmacology* / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009589:Nitrogen Oxides; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D006454:Hemoglobins; D006834:Hydrazines; D020030:Nitric Oxide Donors; D009589:Nitrogen Oxides; D009569:Nitric Oxide; D004533:Egtazic Acid; D019284:Thapsigargin; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D004072:Digitonin; D002118:Calcium