Involvement of ATP-sensitive K+ channels in free radical-mediated inhibition of insulin secretion in rat pancreatic beta-cells.
To explore the mechanisms of inhibition of insulin secretion in pancreatic beta-cells by oxygen free radicals, we studied the effects of H2O2 on membrane currents using the patch-clamp technique. Exposure of beta-cells to H2O2 (> or = 30 mumol/l) increased the activity of ATP-sensitive potassium (K+ATP) channels without changing the single channel conductance in cell-attached membrane patches. Action currents observed during superfusion of 11.1 mmol/l glucose were suppressed. In inside-out membrane patches, the activity of K+ATP channels was not influenced by H2O2. In conventional whole-cell clamp experiments using a pipette solution containing 3 mmol/l ATP, H2O2 did not influence the membrane currents. However, H2O2 did activate the K+ATP channel current in perforated whole-cell clamp configurations. The increased K+ATP channel current was reversed by subsequent exposure to 11.1 mmol/l 2-ketoisocaproic acid. In cell-attached membrane patches, the K+ATP channel current evoked by exposure to 30 mumol/l H2O2 was inhibited by exposure to 11.1 mmol/l glyceraldehyde, whereas the channel was again activated by exposure to 0.3 mmol/l H2O2. Subsequent superfusion of 11.1 mmol/l 2-ketoisocaproic acid inhibited the channel; this effect was counteracted by exposure to 10 mmol/l H2O2. Transient inhibition of K+ATP channels with provocation of action potentials was observed after washout of 100 mumol/l H2O2 during superfusion of 2.8 or 11.1 mmol/l glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
Nakazaki
M
M
First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Japan.
Kakei
M
M
Koriyama
N
N
Tanaka
H
H
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D005609:Free Radicals / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014044:Tolbutamide / Q000494:pharmacology
D005609:Free Radicals; D015221:Potassium Channels; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D006861:Hydrogen Peroxide; D005947:Glucose