Increased calcium-channel currents of pancreatic beta cells in neonatally streptozocin-induced diabetic rats.
Using a whole-cell patch-clamp technique, voltage-dependent Ca(2+)-channel activities were found to be increased in cultured single beta cells isolated from neonatally streptozocin-induced diabetic rats (NSZ rats). The current-voltage relationship and inactivation time course of Ba2+ currents via L-type Ca2+ channels were indistinguishable between NSZ and control rats. However, the current density observed in NSZ rats was significantly greater than that in control rats. Ba2+ currents via T-type Ca2+ channels were also found to be enhanced in NSZ beta cells. The insulin-secretory capacity of cultured pancreatic islets in response to a depolarizing stimulus (20 mmol/L arginine or 30 mmol/L KCl) in the presence of 11.1 mmol/L glucose was augmented in NSZ rats, whereas that in response to 11.1 and 16.7 mmol/L glucose alone was significantly reduced. It is concluded that the impaired insulinotropic action of glucose in beta cells in NSZ rats is not due to reduced activity of voltage-dependent Ca2+ channels. The fact that insulin secretion induced by a depolarizing stimulus was enhanced in NSZ rats may be related to the augmented activity of the voltage-dependent calcium current found in NSZ beta cells.
Kato
S
S
Department of Metabolism and Clinical Nutrition, Kyoto University School of Medicine, Japan.
Ishida
H
H
Tsuura
Y
Y
Okamoto
Y
Y
Tsuji
K
K
Horie
M
M
Okada
Y
Y
Seino
Y
Y
D000818:Animals; D000831:Animals, Newborn; D001464:Barium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007473:Ion Channels / Q000502:physiology; D007515:Islets of Langerhans / Q000502:physiology*; D008297:Male; D009568:Nitrendipine / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar
D015220:Calcium Channels; D007328:Insulin; D007473:Ion Channels; D001464:Barium; D009568:Nitrendipine