An acute insulin secretory response to glucose by pancreatic β cells is critical for preventing sustained post-prandial elevation of blood glucose and free fatty acids, which are detrimental factors in development of diabetes. Short heterodimer partner (SHP) is an orphan nuclear receptor of unknown function in diabetes (Lee et al. 1998). We investigated the potential effect of SHP on glucose responses in β cells (Shin et al. 2001) overexpressing mitochondrial uncoupling protein (UCP2) (Patane et al. 2002).

Islets of Langerhans were isolated from the pancreas of male Sprague-Dawley rats by collagenase digestion technique. Animals were Nembutal (1 mg/kg, I.P.) anaesthetized and then humanely killed by exsanguinations. Separate single β cells or islets were infected with adenoviruses expressing Ad-Null, Ad-SHP, Ad-UCP2, or Ad-UCP2+SHP. Virus-treated dishes were incubated for 2 h in a humidified incubator at 37°C in 5 % CO₂ and balanced air. They were maintained for 48 h after infection for the experiments. The cell-attached configuration of the conventional patch-clamp technique was used. The extent of K_ATP channel activity was expressed as Po (open probability). The relative channel activity in the presence of glucose or methylpyruvate was described as Po/Poc, where Poc is the Po recorded just before drug administration. Insulin secretory capacity was measured using the batch incubation method and RIA. Microfluorescent imaging of [Ca²⁺]c was performed on β cells loaded with the calcium indicator dye Fura-2 acetoxymethyl (Fura-2/AM) ester. Statistical significance was evaluated using an unpaired Student’s t test, and P < 0.05 was considered significant.

In the cell-attached mode, inhibition of K_ATP channel activity at 10 mmol/l glucose application was much greater in SHP-overexpressing (Ad-SHP) β cells than in Ad-Null control. Glucose-stimulated [Ca²⁺]c increase and insulin secretion were also greater in Ad-SHP cells. Impairment of glucose responses through K_ATP channel-dependent pathway in Ad-UCP2 cells was remarkably recovered by the concomitant overexpression of SHP (Ad-UCP2+SHP). The enhanced insulin secretion was not affected by the pretreatment of a PPAR-λ antagonist GW 9662. Methylpyruvate-stimulated K_ATP channel inhibition and insulin secretion were also enhanced in Ad-UCP2+SHP compared to Ad-UCP2, suggesting that SHP may act on downstream of glycolysis.

Our results show that up-regulation of SHP gene in β cells may increase acute insulin secretory response to glucose.

This work was supported by grant No. (R05-2002-000-00558-0) of the KOSEF.

All procedures accord with current national and local guidelines