Free radical-mediated tolbutamide desensitization of K+ATP channels in rat pancreatic beta-cells
| Autor: | Katsumi Aso, Chuwa Tei, Toshihiko Yada, Kazuro Yaekura, Michiyo Fukudome, Mitsuhiro Nakazaki, Masafumi Kakei, Nobuyuki Koriyama, Seiki Ito, Hiroshi Hashiguchi |
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| Rok vydání: | 2001 |
| Předmět: |
medicine.medical_specialty
Patch-Clamp Techniques Potassium Channels Free Radicals Endocrinology Diabetes and Metabolism Radical medicine.medical_treatment Tolbutamide Islets of Langerhans Endocrinology Adenosine Triphosphate Internal medicine Pancreatic beta Cells medicine Animals Hypoglycemic Agents Patch clamp Rats Wistar IC50 Desensitization (medicine) Chemistry Electric Conductivity Drug Tolerance Hydrogen Peroxide Rats Adenosine Diphosphate Membrane Cytoplasm Biophysics medicine.drug |
| Zdroj: | Endocrine journal. 48(3) |
| ISSN: | 0918-8959 |
| Popis: | To study the effects of hydroxyl radicals on the sensitivity of the ATP-sensitive K+ (K+ ATP) channel to tolbutamide, we used patch clamp and microfluorometric techniques in pancreatic beta-cells isolated from rats. cell-attached membrane patches, exposure of the cells to 0.3 mM H2O2 increased the probability of opening of K+ATP channels in the presence of 2.8 mM glucose. Tolbutamide dose-dependently inhibited the K+ATP channel with half-maximal inhibition (IC50) at 0.8 microM before and immediately after exposure to H2O2. After prolonged exposure (>20 min) to H2O2, the IC50 was increased to 15 microM. The presence of both ATP and ADP at concentrations ranging from 0.01 to 0.1 mM in the inside-out bath solution significantly enhanced the inhibition of the channels by 10 microM tolbutamide. Addition of 0.3 mM H2O2 induced a transient minute increase in the cytoplasmic Ca2+ concentration ([Ca2+]i) within 10 min, followed by a sustained pronounced increase in [Ca2]i. After more than 20 min of exposure of cells to 0.3mM H2O2, [Ca2]i was increased to above 2 microM. Treatment of the cytoplasmic face of inside-out membrane patches with 1 microM Ca2+ attenuated the tolbutamide-sensitivity of the K+ATP channel, but not the ATP-sensitivity of the channel. These findings indicate that H2O2 reduces tolbutamide sensitivity by inducing a sustained increase in [Ca2+]i. |
| Databáze: | OpenAIRE |
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