A calorimetric method has been investigated for the determination of the thermodynamic parameters of acid dissociations in dipolar aprotic solvents. For the dissociations of monoprotonated bases BH+ (B: aniline, pyridine, triethylamine, tributylamine, triethanolamine, 1,3-diphenylguanidine and 1,1,3,3-tetramethylguanidine) in N,N-dimethylformamide, dimethyl sulfoxide (DMSO), acetonitrile and propylene carbonate, the solutions of the bases were titrated with small volumes of a “strong acid,” trifluoromethanesulfonic acid. In each solvent, there was an approximately linear relation of unit slope between ΔH298° and ΔG298° showing that the difference in pKa between different BH+’s can mainly be attributed to the difference in the enthalpy term. As for the solvent effect on pKa, however, the entropy term seems to play an important role. A preliminary study has shown that the calorimetric method is also applicable to the dissociations of HX-type weak acids (benzoic and salicylic acids in DMSO, for example), if the dissociation equilibria are not complicated by such reactions as homoconj ugation.

Recent studies have demonstrated the importance of insulin or insulin-like growth factor 1 (IGF-1) for regulation of pancreatic ␤-cell mass. Given the role of tuberous sclerosis complex 2 (TSC2) as an upstream molecule of mTOR (mammalian target of rapamycin), we examined the effect of TSC2 deficiency on ␤-cell function. Here, we show that mice deficient in TSC2, specifically in pancreatic ␤ cells (␤TSC2 ؊/؊ mice), manifest increased IGF-1-dependent phosphorylation of p70 S6 kinase and 4E-BP1 in islets as well as an initial increased islet mass attributable in large part to increases in the sizes of individual ␤ cells. These mice also exhibit hypoglycemia and hyperinsulinemia at young ages (4 to 28 weeks). After 40 weeks of age, however, the ␤TSC2 ؊/؊ mice develop progressive hyperglycemia and hypoinsulinemia accompanied by a reduction in islet mass due predominantly to a decrease in the number of ␤ cells. These results thus indicate that TSC2 regulates pancreatic ␤-cell mass in a biphasic manner.

The total mass of islets of Langerhans is reduced in individuals with type 2 diabetes, possibly contributing to the pathogenesis of this condition. Although the regulation of islet mass is complex, recent studies have suggested the importance of a signaling pathway that includes the insulin or insulin-like growth factor-1 receptors, insulin receptor substrate and phosphatidylinositol (PI) 3-kinase. 3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a serine-threonine kinase that mediates signaling downstream of PI 3-kinase. Here we show that mice that lack PDK1 specifically in pancreatic beta cells (betaPdk1-/- mice) develop progressive hyperglycemia as a result of a loss of islet mass. The mice show reductions in islet density as well as in the number and size of cells. Haploinsufficiency of the gene for the transcription factor Foxo1 resulted in a marked increase in the number, but not the size, of cells and resulted in the restoration of glucose homeostasis in betaPdk1-/- mice. These results suggest that PDK1 is important in maintenance of pancreatic cell mass and glucose homeostasis.

No abstract

No abstract