Nitric oxide (NO) has been implicated as a mediator of Ca2+ entry in response to Ca2+ store depletion (store-operated channels; SOCs), possibly by increasing cGMP. The present studies investigated the action or NO donors and cGMP on cytosolic Ca2+ and revealed rapid and profound actions of NO on possible direct activation of Ca2+ entry channels. The potent NO donor, GEA3162, a 4-aryl-substituted oxatriazol. rapidly activated (within 1 min) a transient increase in intracellular free Ca 2+ in DDTMF-2 cells. The effect was due to activation of Ca 2+ influx since no effect of GEA3162 was observed in Ca 2+-free medium. After GEA3162-treatment of cells in the absence of external Ca1' reapplication of Ca2+ resulted in an immediate and large increase in cytosolic Ca2+ indicating that the entry mechanism remained in an activated state but was rapidly deactivated. To determine whether this influx was related to SOC activity, experiments investigated the effects of the imidazole derivative, SKF96365, a known SOC inhibitor. After thapsigarain treatment, SOC-induced Ca2+ entry activated by depletion of external Ca2+ was blocked by 200 μM SKF96365; in contrast, GEA3162-induced Ca2+ influx was unaffected by SKF96365. Moreover, the action of GEA3162 was not inhibited by the guanylate cyclase inhibitor, LY83583, suggesting that NO-induced Ca2+ entry is not mediated via changes in cGMP levels. No change in the level of cGMP could be detected in response to GEA3162. Permeability to other divalent cation was assessed. Ca2+ influx was totally blocked by La3+. GEA3162 induced Ni2+ entry but only in the presence of Ca2+; this indicates that Ca 2+ is required for activation of the NO-induced channel. The results reveal that NO can induce a rapid and profound influx of Ca2+ via a mechanism independent of store-filling and distinct from SOC-medlated Ca 2+ entry channels. The action of NO does not appear to be mediated by cGMP, and could reflect a more direct interaction perhaps via S-nitrosylation of an entry channel or regulatory proteins thereof.
|Published - 1997
All Science Journal Classification (ASJC) codes
- Agricultural and Biological Sciences (miscellaneous)
- General Biochemistry, Genetics and Molecular Biology
- Cell Biology