Parallel Stimulation of Glucose and Mg2 Accumulation by Insulin in Rat Hearts and Cardiac Ventricular Myocytes

• Published in: Circulation research Vol. 86; no. 3; pp. 326 - 333
• Main Authors: Romani, Andrea M. P, Matthews, Veronica D, Scarpa, Antonio
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 18-02-2000; Lippincott; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Heart; Vertebrates: cardiovascular system; Heart; Pancreatic hormone; Rat; Biological transport; Rodentia; Stimulation; Heart ventricle; Glucose; Insulin; Uptake; Myocyte; Vertebrata; Mammalia; Animal; Magnesium ion; Carbohydrate; Circulatory system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.86.3.326

ABSTRACTThe stimulation of β-adrenoceptors in cardiac cells results in a rapid loss of cellular Mg. Because insulin physiologically counteracts several of the cellular effects mediated by the activation of β-adrenoceptors and the elevation of cytosolic cAMP levels, we investigated whether insulin administration could prevent Mg mobilization from rat hearts and ventricular myocytes. Rat hearts were perfused in a retrograde Langendorff system, and the changes in extracellular Mg were measured by atomic absorbance spectrophotometry. Pretreatment of the hearts with 6 nmol/L insulin completely prevented the Mg extrusion induced by the β-adrenergic agonist isoproterenol. Furthermore, the administration of insulin per se induced an accumulation of Mg by the heart. This accumulation was small but detectable in the presence of 25 to 35 μmol/L [Mg]o and increased in proportion to [Mg]o. Insulin-mediated Mg accumulation was not observed in hearts perfused with a medium devoid of glucose or with a medium containing the inhibitors of glucose transport, cytochalasin B and phloretin. Insulin-stimulated [H]2-deoxyglucose accumulation was measured in collagenase-dispersed cardiac ventricular myocytes in the presence of varying levels of [Mg]o. Glucose transport was not observed below 25 μmol/L [Mg]o, and it also increased in proportion to [Mg]o. Taken together, these results indicate the presence of a major uptake of Mg into cardiac cells that is stimulated by insulin and may require the insulin-induced operation of a glucose transporter. Hence, extracellular and/or intracellular Mg may modulate glucose transport and/or utilization.