Cyclic GMP inhibits cytoplasmic Ca2+ oscillation by increasing Ca2+-ATPase activity in rat megakaryocytes.
The regulatory effects of cyclic GMP on purinoceptor-operated cytoplasmic Ca2+ oscillation of rat megakaryocytes were investigated by using whole-cell patch-clamp technique. ATP-induced oscillatory K+ currents though Ca2+-activated K+ channels (I(KCa)S) were depressed by pretreatment with the guanylate cyclase activator, sodium nitroprusside, and a stable membrane-permeable cGMP analogue, 8-bromo-cGMP. The inhibition by sodium nitroprusside was blocked by treatment with a cyclic nucleotide-dependent protein kinase inhibitor, N-[2-(methylamino)]-5-isoquinolinesulfonamide x HCl (H-8) (10 microM), but not by a selective cAMP-dependent-protein kinase inhibitor, Rp-cAMPS (100 microM). The oscillatory I(KCa) directly evoked by intracellular D-myo-inositol-trisphosphate (IP3) perfusion was also inhibited by the application of sodium nitroprusside. The inhibitory effect of sodium nitroprusside disappeared when the ATP-induced oscillatory I(KCa) was changed to a monophasic sustained I(KCa) current by inhibition of Ca2+-ATPase. These results suggested that cGMP depressed Ca2+ mobilization by improving Ca2+-ATPase activity by phosphorylation.
Uneyama
C
C
Division of Pathology, National Institute of Health Sciences, Tokyo, Japan.
Uneyama
H
H
Akaike
N
N
Takahashi
M
M
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D017867:Cyclic Nucleotide-Regulated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008533:Megakaryocytes / Q000201:enzymology*; D008564:Membrane Potentials / Q000187:drug effects; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D000959:Antihypertensive Agents; D009599:Nitroprusside; D017867:Cyclic Nucleotide-Regulated Protein Kinases; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D002118:Calcium