Article date: January 2000
By: Sirintorn Yibchok‐anun, Henrique Cheng, Ter‐Hsin Chen, Walter H Hsu, in Volume 129, Issue 2, pages 257-264
The mechanisms underlying AVP‐induced increase in [Ca2+]i and glucagon release in clonal α‐cells In‐R1‐G9 were investigated.
AVP increased [Ca2+]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.
In Ca2+‐containing medium, AVP increased [Ca2+]i in a biphasic pattern; a peak followed by a sustained plateau. In Ca2+‐free medium, the Ca2+ 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 Ca2+. When [Ca2+]i was stringently deprived by BAPTA, a Ca2+ chelator, AVP still significantly increased glucagon release.
Pretreatment with thapsigargin, a microsomal Ca2+ ATPase inhibitor, abolished both the Ca2+ peak and sustained plateau.
AVP increased intracellular concentration of IP3.
U‐73122 (8 μM), a phospholipase C inhibitor, abolished AVP‐induced increases in [Ca2+]i, but only reduced AVP‐induced glucagon release by 39%.
Pretreatment with nimodipine, an L‐type Ca2+ channel blocker failed to alter AVP‐induced glucagon release or increase in [Ca2+]i.
The results suggest that AVP causes glucagon release through both Ca2+‐dependent and ‐independent pathways. For the Ca2+‐dependent pathway, the Gq protein activates phospholipase C, which catalyzes the formation of IP3. IP3 induces Ca2+ release from the endoplasmic reticulum, which, in turn, triggers Ca2+ influx. Both Ca2+ release and Ca2+ influx may contribute to AVP‐induced glucagon release.
The mechanisms underlying AVP‐induced increase in [Ca2+]i and glucagon release in clonal α‐cells In‐R1‐G9 were investigated.
AVP increased [Ca2+]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.
In Ca2+‐containing medium, AVP increased [Ca2+]i in a biphasic pattern; a peak followed by a sustained plateau. In Ca2+‐free medium, the Ca2+ 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 Ca2+. When [Ca2+]i was stringently deprived by BAPTA, a Ca2+ chelator, AVP still significantly increased glucagon release.
Pretreatment with thapsigargin, a microsomal Ca2+ ATPase inhibitor, abolished both the Ca2+ peak and sustained plateau.
AVP increased intracellular concentration of IP3.
U‐73122 (8 μM), a phospholipase C inhibitor, abolished AVP‐induced increases in [Ca2+]i, but only reduced AVP‐induced glucagon release by 39%.
Pretreatment with nimodipine, an L‐type Ca2+ channel blocker failed to alter AVP‐induced glucagon release or increase in [Ca2+]i.
The results suggest that AVP causes glucagon release through both Ca2+‐dependent and ‐independent pathways. For the Ca2+‐dependent pathway, the Gq protein activates phospholipase C, which catalyzes the formation of IP3. IP3 induces Ca2+ release from the endoplasmic reticulum, which, in turn, triggers Ca2+ influx. Both Ca2+ release and Ca2+ influx may contribute to AVP‐induced glucagon release.
British Journal of Pharmacology (2000) 129, 257–264; doi:10.1038/sj.bjp.0703037
DOI: 10.1038/sj.bjp.0703037
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