First phase of glucose-stimulated insulin secretion from MIN 6 cells does not always require extracellular calcium influx.
To demonstrate an involvement of ATP-sensitive potassium (K(ATP)) channel-independent pathways in the first phase of glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells, the time course of GSIS from MIN6 cells was analyzed at 30-s sample intervals. GSIS was biphasic with the first phase being observed 120 to 390 s after glucose addition, peaking at 180 s, and with a shoulder at 240 to 330 s. Both 10 microM diazoxide and 3 microM verapamil completely inhibited tolbutamide- or glibenclamide-induced insulin secretion and suppressed the peak of the first phase of GSIS, but did not result in complete suppression. The shoulder following the peak was suppressed by 1 muM dantrolene. The peak, but not shoulder, disappeared under the extracellular Ca2+-free condition. A significant amount of insulin secretion remained even in the combined presence of verapamil and dantrolene. The Na+ channel blocker tetrodotoxin (30 nM) nearly completely inhibited the first phase release. These results suggest that the first phase of GSIS from MIN6 cells depends on both Ca2+-dependent and -independent mechanisms. The former mechanism includes the extracellular Ca2+ influx via L-type voltage-dependent calcium channel and intracellular Ca2+ release from endoplasmic reticulum via ryanodine receptors, and the latter mechanism involves the pathways associated with Na+ channels.
Shigeto
Makoto
M
Division of Diabetes and Endocrinology, Department of Medicine, Kawasaki Medical School, Kurashiki, Okayama, Japan.
Katsura
Masashi
M
Matsuda
Masafumi
M
Ohkuma
Seitaro
S
Kaku
Kohei
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002127:Calcium Isotopes; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003620:Dantrolene / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D007329:Insulin Antagonists / Q000494:pharmacology; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D051379:Mice; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002127:Calcium Isotopes; D007328:Insulin; D007329:Insulin Antagonists; D015221:Potassium Channels; D015222:Sodium Channels; D013779:Tetrodotoxin; D014044:Tolbutamide; D014700:Verapamil; D007770:L-Lactate Dehydrogenase; D003620:Dantrolene; D005947:Glucose; D003981:Diazoxide; D005905:Glyburide; D002118:Calcium