Potentiation of sulfonylurea action by an EPAC-selective cAMP analog in INS-1 cells: comparison of tolbutamide and gliclazide and a potential role for EPAC activation of a 2-APB-sensitive Ca2+ influx.
Tolbutamide and gliclazide block the K(ATP) channel K(ir)6.2/Sur1, causing membrane depolarization and stimulating insulin secretion in pancreatic beta cells. We examined the ability of the EPAC-selective cAMP analog 8-pCPT-2'-O-Me-cAMP-AM to potentiate the action of these drugs and the mechanism that might account for it. Insulin secretion stimulated by both 200 μM tolbutamide and 20 μM gliclazide, concentrations that had equivalent effects on membrane potential, was inhibited by thapsigargin (1 μM) or the L-type Ca(2+) channel blocker nicardipine (2 μM) and was potentiated by 8-pCPT-2'-O-Me-cAMP-AM at concentrations ≥2 μM in INS-1 cells. Ca(2+) transients stimulated by either tolbutamide or gliclazide were inhibited by thapsigargin or nicardipine and were significantly potentiated by 8-pCPT-2'-O-Me-cAMP-AM at 5 μM but not 1 μM. Both tolbutamide and gliclazide stimulated phospholipase C activity; however, only gliclazide did so independently of its activity at K(ATP) channels, and this activity was partially inhibited by pertussis toxin. 8-pCPT-2'-O-Me-cAMP-AM alone (5 μM) did not stimulate insulin secretion, but did increase intracellular Ca(2+) concentration significantly, and this activity was inhibited by 25 μM 2-aminoethoxydiphenylborate (2-APB) or the removal of extracellular Ca(2+). 8-pCPT-2'-O-Me-cAMP-AM potentiation of insulin secretion stimulated by tolbutamide was markedly inhibited by 2-APB (25 μM) and enhanced by the PKC inhibitor bisindolylmaleimide I (1 μM). Our data demonstrate that the actions of both tolbutamide and gliclazide are strongly potentiated by 8-pCPT-2'-O-Me-cAMP-AM, that gliclazide can stimulate phospholipase C activity via a partially pertussis toxin-sensitive mechanism, and that 8-pCPT-2'-O-Me-cAMP-AM potentiation of tolbutamide action may involve activation of a 2-APB-sensitive Ca(2+) influx.
Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, USA.
Rachel E
RE
Jarrard
Yuchen
Y
Wang
Amy E
AE
Salyer
Evan P S
EP
Pratt
Ian M
IM
Soderling
Marcy L
ML
Guerra
Allison M
AM
Lange
Hilary J
HJ
Broderick
Gregory H
GH
Hockerman
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D004789:Enzyme Activation; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D005907:Gliclazide / Q000494:pharmacology*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D042541:Intracellular Space / Q000378:metabolism; D054086:KATP Channels / Q000502:physiology; D008301:Maleimides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D051381:Rats; D014044:Tolbutamide / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
C555650:8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-monophosphate acetoxymethyl ester; D001896:Boron Compounds; D020746:Calcium Channels, L-Type; D020662:Guanine Nucleotide Exchange Factors; D007004:Hypoglycemic Agents; D007211:Indoles; D007328:Insulin; D054086:KATP Channels; D008301:Maleimides; C442864:RAPGEF4 protein, human; D014044:Tolbutamide; D000242:Cyclic AMP; C109986:2-aminoethoxydiphenyl borate; D010738:Type C Phospholipases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D005907:Gliclazide; C070515:bisindolylmaleimide I; D002118:Calcium