The oxidative metabolism of irbesartan, a new nonpeptide angiotensin II receptor antagonist, was investigated on 12 human fully characterized hepatic microsomes and purified cytochrome P-450 (CYP) isoforms. After incubation of microsomes with irbesartan and NADPH, four main hydroxy metabolites were formed, as confirmed by liquid chromatography-mass spectrometry analysis. Irbesartan oxidation fo...

The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl- channel that is regulated by cAMP-dependent phosphorylation and by intracellular ATP. Intracellular ATP also regulates a class of K+ channels that have a distinct pharmacology: they are inhibited by sulfonylureas and activated by a novel class of drugs called K+ channel openers. In search of modulators of CFTR Cl- channels,...

Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner that is dependent on circulating 17beta-estradiol (E2) and glucose concentrations. However, the intrinsic conductances responsible for the episodic firing pattern underlying pulsatile release and the effects of E2 and glucose on these conductances are primarily unknown. Whole-cell recordings from mouse enhanced green fluore...

Glucose-induced insulin secretion (IS) by β-cells is controlled by two pathways. The triggering pathway involves ATP-sensitive potassium (K(ATP)) channel-dependent depolarization, Ca(2+) influx, and rise in the cytosolic Ca(2+) concentration ([Ca(2+)](c)), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca(2+)](c). After ex...

Rats with or without 0.5% tolbutamide in the diet were iniected over a 5-day period with growth hormone, ACTH, cortisol, dexamethasone, or various mixtures of these diabetogenic hormones and the daily alterations in blood glucose (BG), serum (Sl), and pancreatic insulin (PI) concentrations followed as well as glucosuria. GH (5 mg/day) increased the insulin concentration in the pancreas and seru...

Sulfonylurea derivatives glibenclamide and tolbutamide are selective blockers of ATP-sensitive K+ (KATP) channels. However, their ability to prevent cellular K+ loss and shortening of action potential duration during ischemia or hypoxia in the intact heart is modest compared with their efficacy at blocking KATP channels in excised membrane patches. In the isolated arterially perfused rabbit int...

Disulfiram and its primary metabolite diethyldithiocarbamate are effective mechanism-based inhibitors of cytochrome P-450 2E1 (CYP2E1)1 in vitro. Single-dose disulfiram diminishes CYP2E1 activity in vivo and has been used to identify CYP2E1 participation in human drug metabolism and prevent CYP2E1-mediated toxification. Specificity of single-dose disulfiram toward CYP2E1 in vivo, however, remai...

Mourad NI, Nenquin M, Henquin J.-C. Metabolic amplifying pathway increases both phases of insulin secretion independently of -cell actin microfilaments. Am J Physiol Cell Physiol 299: C389–C398, 2010. First published May 19, 2010; doi:10.1152/ajpcell.00138.2010.— Two pathways control glucose-induced insulin secretion (IS) by -cells. The triggering pathway involves ATP-sensitive potassium (KATP)...

The effect of human serum albumin (Hsa) and human liver cytosol (Hlc) on the in vitro enzyme kinetics of the formation of hydroxytolbutamide (CYP2C9 marker reaction) and the inhibitory effect of gemfibrozil on tolbutamide hydroxylation were examined using human liver microsomes. The addition of Hsa greatly decreased the unbound concentrations of tolbutamide and gemfibrozil in the incubation med...