Mechanisms of AVP-induced glucagon release in clonal alpha-cells in-R1-G9: involvement of Ca(2+)-dependent and -independent pathways.
1. The mechanisms underlying AVP-induced increase in [Ca(2+)](i) and glucagon release in clonal alpha-cells In-R1-G9 were investigated. 2. AVP increased [Ca(2+)](i) and glucagon release in a concentration-dependent manner. After the administration of AVP, glucagon was released within 30 s, quickly reached the maximum within 2 min, and maintained a steady-state concentration for at least 15 min. 3. In Ca(2+)-containing medium, AVP increased [Ca(2+)](i) in a biphasic pattern; a peak followed by a sustained plateau. In Ca(2+)-free medium, the Ca(2+) response to AVP became monophasic with lower amplitude and no plateau. Both the basal and AVP-induced glucagon releases were lower in the absence than in the presence of extracellular Ca(2+). When [Ca(2+)](i) was stringently deprived by BAPTA, a Ca(2+) chelator, AVP still significantly increased glucagon release. 4. Pretreatment with thapsigargin, a microsomal Ca(2+) ATPase inhibitor, abolished both the Ca(2+) peak and sustained plateau. 5.AVP increased intracellular concentration of IP(3). 6. U-73122 (8 microM), a phospholipase C inhibitor, abolished AVP-induced increases in [Ca(2+)](i), but only reduced AVP-induced glucagon release by 39%. 7. Pretreatment with nimodipine, an L-type Ca(2+) channel blocker failed to alter AVP-induced glucagon release or increase in [Ca(2+)](i). 8. The results suggest that AVP causes glucagon release through both Ca(2+)-dependent and -independent pathways. For the Ca(2+)-dependent pathway, the G(q) protein activates phospholipase C, which catalyzes the formation of IP(3). IP(3) induces Ca(2+) release from the endoplasmic reticulum, which, in turn, triggers Ca(2+) influx. Both Ca(2+) release and Ca(2+) influx may contribute to AVP-induced glucagon release.
Yibchok-Anun
S
S
Department of Biomedical Sciences, Iowa State University, Ames, IA 50011-1250, USA.
Cheng
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H
Chen
T H
TH
Hsu
W H
WH
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D002999:Clone Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005934:Glucagon / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D009553:Nimodipine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D012076:Renal Agents / Q000494:pharmacology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D000590:Amino Acid Chloromethyl Ketones; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D004963:Estrenes; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D012076:Renal Agents; D015842:Serine Proteinase Inhibitors; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D001127:Arginine Vasopressin; C074854:U 73343; C070517:carbobenzyloxyleucyl-tyrosine chloromethyl ketone; D009553:Nimodipine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D005934:Glucagon; D000242:Cyclic AMP; D002118:Calcium