Mechanisms of bradykinin-induced insulin secretion in clonal beta cell line RINm5F.
We investigated the mechanisms underlying bradykinin (BK)-induced rise in intracellular Ca++ concentration [Ca++]i and insulin secretion using clonal beta cell line RINm5F. Incubation with a range of concentrations of BK increased in concentration-dependent manners both insulin secretion (BK of 10 nM to 10 microM) and [Ca++]i (BK of 100 nM to 100 microM). In Ca++-containing medium, BK (1 microM) induced a biphasic [Ca++]i rise, which was characterized by a Ca++ peak and a sustained Ca++ phase. In the Ca++-free medium, BK failed to increase insulin secretion and induced only a Ca++ peak without the sustained Ca++ phase. Thapsigargin (1 microM), an inhibitor of the Ca++ pump in the endoplasmic reticulum, abolished the Ca++ peak and the sustained phase. Nimodipine (1 microM), a voltage-dependent Ca++ channel blocker, abolished the BK-induced sustained Ca++ phase and inhibited BK-induced insulin release. The BK1 receptor agonist des-Arg9-BK (1 microM) did not change either [Ca++]i or insulin secretion. Both the BK-induced insulin secretion and rise in [Ca++]i were inhibited by a selective BK2 receptor antagonist, HOE 140 (3.3-100 nM), in concentration-dependent manners but were not by a BK1 receptor antagonist des-Arg9,Leu8-BK (1 microM). Pretreatment with pertussis toxin (0.1 microg/ml) did not block the BK-induced insulin secretion or increase in [Ca++]i. U-73122 (4, 6 and 8 microM), a phospholipase C inhibitor, antagonized both the BK-induced insulin secretion and the increase in [Ca++]i in a concentration-dependent and parallel manner. BK increased intracellular concentrations of inositol-1,4,5-trisphosphate (IP3). Neither (p-amylcinnamoyl)anthranilic acid (100 microM), a phospholipase A2 inhibitor, nor N(G)-nitro-L-arginine methylester (100 microM), a nitric oxide synthase inhibitor, inhibited these effects of BK. Taken together, these findings suggested that in beta cells, BK activates BK2 receptors, which, in turn, activate a pertussis toxin-insensitive G protein. The G protein couples to phospholipase C, which promotes the formation of IP3 and diacylglycerol. IP3 releases [Ca++]i from the intracellular Ca++ store, probably the endoplasmic reticulum, which triggers Ca++ influx via voltage-dependent Ca++ channels and thus increases insulin secretion.
Yang
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C
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames 50011, USA.
Lee
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B
Chen
T H
TH
Hsu
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WH
D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004963:Estrenes / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D037342:Pertussis Toxin; D011760:Pyrrolidinones / Q000494:pharmacology; D018002:Receptors, Bradykinin / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004963:Estrenes; D007328:Insulin; D011760:Pyrrolidinones; D018002:Receptors, Bradykinin; D010566:Virulence Factors, Bordetella; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D009553:Nimodipine; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D001920:Bradykinin; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester