title: Intracellular mechanisms of cytoplasmic Ca2+ oscillation in rat megakaryocyte.
abstract: Extracellular application of ATP and ADP evoked the oscillatory K+ currents (IKCa) resulting from the periodic rise in cytoplasmic Ca2+ concentration ([Ca2+]i) of megakaryocyte isolated from rat bone marrow (Uneyama, H., Uneyama, C., and Akaike, N. (1992) Jpn. J. Pharmacol. 58, 231). The intracellular mechanism of ATP-induced cytoplasmic Ca2+ oscillation was investigated by the use of nystatin-perforated patch-clamp technique. Caffeine and ryanodine, which release Ca2+ from the Ca(2+)-induced Ca2+ release pool (CICR), and procaine, a blocker of Ca2+ release from CICR, had no effect on the IKCa oscillation in megakaryocyte. Thapsigargin and A23187 activated IKCa irreversibly by mobilizing Ca2+, but under Ca(2+)-free conditions they activated IKCa transiently. Intracellular application of inositol 1,4,5-triphosphate (IP3) also induced IKCa oscillation. Phorbol myristate acetate (PMA), a strong activator of protein kinase C (PKC), inhibited the oscillation completely. The inhibitory action of PMA was reversed by an inhibitor of PKC, staurosporin. The oscillation of ATP-induced IKCa was disrupted by staurosporin or calmodulin (CaM) antagonists such as W-7 and trifluoperazine, resulting in a transient and successive plateau-like IKCa. These results suggest that Ca2+ oscillation in megakaryocyte is caused by the interaction of both the Ca2+ release from IP3-sensitive Ca2+ pool and the Ca2+ uptake stimulated by PKC and Ca2+/CaM complex. Furthermore, forskolin, an activator of adenylate cyclase, and isobutylmethylxanthin, an inhibitor of phosphodiesterase, inhibited the frequency, latency, and current amplitude of the oscillation in a concentration-dependent manner. These reagents inhibited IP3-induced oscillation as well as an ATP-induced oscillation. Thus, the ATP-induced [Ca2+]i oscillation of rat megakaryocyte is also modulated by cAMP.
authors.affiliation: Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Uneyama
authors.forename: C
authors.initials: C
authors.lastname: Uneyama
authors.forename: N
authors.initials: N
authors.lastname: Akaike
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000037:antagonists & inhibitors; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008533:Megakaryocytes / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008954:Models, Biological; D009991:Oscillometry; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D019311:Staurosporine; D013449:Sulfonamides / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D002147:Calmodulin; D013449:Sulfonamides; D013729:Terpenes; D005576:Colforsin; D014268:Trifluoperazine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000001:Calcimycin; D004533:Egtazic Acid; C017967:W 7; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases; D019311:Staurosporine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine