Sulfonylureas activate glycogen phosphorylase and increase cytosolic free-Ca2+ levels in isolated rat hepatocytes

Sulfonylurea effects on acid and pepsinogen secretion in isolated rabbit gastric glands

The influence of different sulfonylureas on the rate of acid and pepsinogen secretion was studied in isolated rabbit gastric glands. Neither tolbutamide (10-500 microM), chlorpropamide (10-500 microM), glibenclamide (1-50 microM) nor glipizide (1-50 microM) exerted a secretory effect. In contrast, gliquidone caused a marked and dose-dependent stimulation of acid production in gastric glands incubated under basal conditions and potentiated the stimulatory effect of both histamine and carbachol. Gliquidone also increased the rate of pepsinogen release in gastric glands incubated either under basal conditions or in the presence of cholecystokinin-octapeptide or isoproterenol. The secretory effects of gliquidone were associated with a significant increase in the glandular content of cyclic AMP, caused by a competitive inhibition of low-Km cyclic AMP phosphodiesterase. Our results indicate that, among the assayed sulfonylureas, only gliquidone, in the micromolar range, stimulates acid and pepsinogen secretion through a cyclic AMP-dependent mechanism.

H-ras transfection of the rat kidney cell line NRK-52E results in increased induction of c-fos, c-jun and hsp70 following sulofenur treatment

The effect of the antineoplastic drug sulofenur on the induction of the immediate-early genes (IEG) c-fos and c-jun and the stress gene hsp70 was compared in the rat kidney epithelial-like cell line NRK-52E and a derivative H-ras-transfected (H/1.2NRK-52E) cell line. Fold induction for each gene after sulofenur (500 microM) treatment was greater in H/1.2NRK-52E. The maximum increases for NRK-2E and H/1.2NRK-52E were as follows: c-fos, approximately 10-fold and approximately 18-fold; c-jun, approximately 2.5-fold and approximately 3.6-fold; hsp70, approximately 13-fold and approximately 30-fold. In cells loaded with EGTA/AM or treated in low or no Ca2+ HBSS, c-fos induction was reduced similarly in both cell types. However, inhibition of protein kinases with staurosporin and calphostin C reduced c-fos by 80% in NRK-52E but by only 10-20% in H/1.2NRK.52E. These results indicate that sulofenur-induced IEG elevation is Ca(2+)-dependent and that the requirement for protein kinase C activation is bypassed in H-ras-transfected cells.

Metabolic effects of glibenclamide in isolated rat hepatocytes in the absence of extracellular Ca2+

We examined the metabolic effects of glibenclamide, a potent second-generation sulfonylurea, in isolated rat hepatocytes incubated in the absence of extracellular Ca2+. We first demonstrated in the present study that glibenclamide caused a significant increase in basal glucose release and lactate production without any modification of intracellular Ca2+ concentration or cAMP levels in isolated rat hepatocytes. Furthermore, glibenclamide inhibited the noradrenaline-induced increase in cAMP accumulation, while activation of glycogenolysis by noradrenaline was not suppressed by this agent. Our data indicate that glibenclamide exerts its metabolic effects independent of intracellular Ca2+ mobilization and cAMP accumulation.

Modulation of glycogen phosphorylase activity and fructose 2,6-bisphosphate levels by glibenclamide and meglitinide in isolated rat hepatocytes: a comparative study

The influence of glibenclamide and meglitinide, or 4-[2-(5-chloro-2-methoxybenzamide)ethyl]-benzoic acid, a compound similar to the nonsulfonylurea moiety of glibenclamide, on glycogen phosphorylase a activity, fructose 2,6-bisphosphate (F-2,6-P2) level, and cytoplasmic free-Ca2+ concentration has been studied in isolated rat hepatocytes. Both glibenclamide and meglitinide caused a transient and dose-dependent activation of glycogen phosphorylase, with half-maximal effects corresponding to 3.7 +/- 1.6 and 9.6 +/- 3.3 mumol/L, respectively. This enzyme activation occurred without significant changes in hepatocyte cyclic adenosine monophosphate (cAMP) levels and was accompanied by an increase in cytoplasmic concentration of free Ca2+. Parallel to these effects, glibenclamide increased the cellular content of F-2,6-P2, with this effect being associated with a reduction in the rate of glucose formation from a mixture of [14C]lactate/pyruvate. Under similar conditions, meglitinide caused a significant reduction of F-2,6-P2 levels and accelerated the gluconeogenic flux. The mechanism by which meglitinide decreases hepatocyte F-2,6-P2 levels seems to be mediated by stimulation of fructose-2,6-bisphosphatase. This comparative study may help to elucidate which among the hepatic effects of glibenclamide are exerted specifically by the sulfonylurea moiety.