Evidence of enhancement of malate-aspartate shuttle activity in beta cells of streptozotocin-induced non-insulin-dependent diabetic rats.
Glucose-induced insulin secretion is selectively impaired in beta cells from animals with non-insulin-dependent diabetes mellitus (NIDDM). This study was performed to clarify whether the malate-aspartate shuttle among the glucose metabolic pathways is intact in beta cells of NIDDM rats. The insulin secretory capacity of the islets and the K(ATP) channel activity in single beta cells were measured in control and NIDDM rats injected with streptozotocin (STZ) during the neonatal period, using a radioimmunoassay and patch-clamp technique. The increase of insulin secretion induced by 11.1 mmol/L glucose or 10 mmol/L dihydroxyacetone (DHA) was significantly reduced in NIDDM islets, suggesting an impaired glycerol-phosphate shuttle. The application of glyceraldehyde (10 mmol/L) in NIDDM or control islets elicited an increase in insulin secretion, but the difference between the 2 groups was indistinguishable. On the contrary, the increase of insulin secretion and the inhibition of K(ATP) channel activity induced by aspartate, which preferentially participates in the malate-aspartate shuttle, were significantly greater in NIDDM versus the control. However, intracellularly applied aspartate in the inside-out mode did not inhibit K(ATP) channel activity. These findings show that malate-aspartate shuttle activity is potentiated in pancreatic beta cells of NIDDM rats, suggesting the development of a compensatory mechanism for the reduced activity of the glycerol-phosphate shuttle in NIDDM.
Song
D K
DK
Department of Physiology, Keimyung University School of Medicine, Taegu, South Korea.
Ahn
Y H
YH
Bae
J H
JH
Park
W K
WK
Hong
Y S
YS
Ho
W K
WK
Earm
Y E
YE
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001786:Blood Glucose / Q000032:analysis; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects*; D008293:Malates / Q000494:pharmacology*; D008297:Male; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D007328:Insulin; D008293:Malates; D015221:Potassium Channels; D001224:Aspartic Acid; C030298:malic acid; D000255:Adenosine Triphosphate; D005947:Glucose