Nitric oxide induces transient Ca2+ changes in endothelial cells independent of cGMP.
Ca2+ changes induced by nitric oxide (NO.) were investigated in cultured human endothelial cells. Sodium nitroprusside (SNP) (1-100 mumol/L) and S-Nitroso-N-acetylpenicillamine (SNAP) (100 mumol/L) were used as NO. donors. The cytoplasmatic Ca2+ concentration was calculated using ratiometric FURA2 fluorescence measurements. Both NO. donors caused transient oscillatory Ca2+ changes, which were not detectable in the presence of oxyhemoglobin (50 mumol/L). Digital ratio imaging revealed initiation sites within cells where Ca2+ increases started spreading, which indicates that nonuniformly distributed targets might be involved in these reactions. Calcium was released from intracellular stores as indicated by experiments performed in Ca(2+)-free buffer. L-type Ca(2+)-channel blocker diltiazem (100 mumol/L) was not able to block these responses. NO.-induced Ca2+ release from intracellular stores caused capacitative Ca2+ entry. Both thapsigargin (1 mumol/L) and cyclopiazonic acid (10 mumol/L) inhibited the SNP response completely, whereas neither ryanodine (up to 100 mumol/L) nor dantrolene (100 mumol/L) was able to inhibit Ca2+ changes induced by SNP, indicating that primarily inositol 1,4,5-triphosphate (IP3)-dependent stores are released upon stimulation with NO.. A small inhibitory effect of ATP- and SNP-induced peak [Ca2+]i increase was measured in the presence of both caffeine (20 mmol/L) and procaine (1 mmol/L). Evidence is presented that cGMP is not involved in NO.-induced Ca2+ signals, as neither inhibitors of guanylate cyclase (methylene blue and LY 83583) nor cell permeant analogues of cGMP altered or simulated [Ca2+] changes. An inhibitor of cGMP-dependent protein kinase was also ineffective. We therefore propose that endothelial cells have specific targets proximal or at IP3 receptors to induce Ca2+ changes in endothelial cells stimulated with NO..
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Klinik für Anästhesiologie und Intensivtherapie, Universitätsklinikum Charité Humboldt-Universität zu Berlin, Germany.
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism*; D003620:Dantrolene / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D006162:Guanylate Cyclase / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D011343:Procaine / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D026423:S-Nitroso-N-Acetylpenicillamine; D019284:Thapsigargin / Q000494:pharmacology
D007211:Indoles; D012433:Ryanodine; D009599:Nitroprusside; D009569:Nitric Oxide; D002110:Caffeine; D011343:Procaine; D019284:Thapsigargin; D026423:S-Nitroso-N-Acetylpenicillamine; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D006162:Guanylate Cyclase; D004110:Diltiazem; D003620:Dantrolene; D010396:Penicillamine; D006152:Cyclic GMP; D002118:Calcium; C000543:cyclopiazonic acid