REDUCED SENSITIVITY OF DIHYDROXYACETONE ON ATP-SENSITIVE K+ CHANNELS OF PANCREATIC BETA-CELLS IN GK RATS

In the GK (Goto-Kakizaki) rat, a genetic model of non-insulin-dependent diabetes mellitus, glucose-induced insulin secretion is selectively impaired. In addition, it has been suggested by previous studies that impaired glucose metabolism in beta cells of the GK rat results in insufficient closure of ATP-sensitive K+ channels (K-ATP channels) and a consequent decrease in depolarization, leading to a decreased insulin release. We have recently reported that the site of disturbed glucose metabolism is probably located in the early stages of glycolysis or in the glycerol phosphate shuttle. In the present study, in order to identify the impaired metabolic step in diabetic beta cells, we have investigated insulin secretory capacity by stimulation with dihydroxyacetone (DHA), which is known to be directly converted to DHA-phosphate and to preferentially enter the glycerol phosphate shuttle. In addition, using the patch-clamp technique, we also have studied the sensitivity of DHA on the K-ATP channels of beta cells in GK rats. The insulin secretion in response to 5 mmol/l DHA with 2.8 mmol/l glucose was impaired, and DHA sensitivity of the K-ATP channels was reduced in beta cells of GK rats. From these results, we suggest that the intracellular site responsible for impaired glucose metabolism in pancreatic beta cells of GK rats is located in the glycerol phosphate shuttle.