Endogenous somatostatin receptors mobilize calcium from inositol 1,4,5-trisphosphate-sensitive stores in NG108-15 cells.
Somatostatin receptors are members of the G-protein-coupled receptor superfamily and exert their principal effects by coupling to inhibitory G-proteins. We used fura-2-based digital calcium imaging and assayed for [3H]inositol phosphates (IPs) to study the effects of somatostatin on intracellular calcium signaling in neuroblastomaxglioma NG108-15 cells. Both somatostatin-14 and octreotide induced concentration-dependent increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Thirty-four percent of the cells responded to treatment with 100 nM somatostatin-14. Somatostatin-induced responses were not blocked by the removal of extracellular calcium; instead, they were abolished by pretreatment with 100 nM thapsigargin, an agent that depletes and prevents refilling of intracellular Ca(2+) stores. Pretreatment with the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist xestospongin C (10 microM) for 20 min inhibited markedly the somatostatin-induced response. Somatostatin (100 nM) increased [3H]IPs formation. U73122 (1 microM), an inhibitor of phospholipase C (PLC), completely blocked the somatostatin-induced [Ca(2+)](i) increases and the formation of [3H]IPs. Pretreatment with pertussis toxin (PTX, 200 ng/ml) for 24 h blocked the somatostatin-induced responses. Thus, we conclude that activation of endogenous somatostatin receptors in NG108-15 cells induces the release of calcium from IP(3)-sensitive intracellular stores through PTX-sensitive G-protein-coupled PLC.
Rhie
Duck-Joo
DJ
Department of Physiology, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, South Korea.
Sung
Jong-Ho
JH
Ha
U-Sin
US
Kim
Hee Jung
HJ
Min
Do Sik
DS
Hahn
Sang June
SJ
Kim
Myung-Suk
MS
Jo
Yang-Hyeok
YH
Yoon
Shin Hee
SH
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D004963:Estrenes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D005910:Glioma / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D007293:Inosine Triphosphate / Q000502:physiology*; D047028:Macrocyclic Compounds; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism; D015282:Octreotide / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D017481:Receptors, Somatostatin / Q000819:agonists / Q000187:drug effects*; D013004:Somatostatin / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D004963:Estrenes; D047028:Macrocyclic Compounds; D010080:Oxazoles; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D017481:Receptors, Somatostatin; C108644:xestospongin A; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D007293:Inosine Triphosphate; C074854:U 73343; D013004:Somatostatin; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D015282:Octreotide; D002118:Calcium