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(Hypertension. 2001;38:612.)
© 2001 American Heart Association, Inc.

Cardiovascular Biology

Altered Cellular Magnesium Responsiveness to Hyperglycemia in Hypertensive Subjects

Mario Barbagallo; Ligia J. Dominguez; Orit Bardicef; Lawrence M. Resnick

From the Institute of Internal Medicine and Geriatrics, University of Palermo (M.B., L.J.D.), Italy; and Hypertension Center, New York Presbyterian Hospital/Weill Medical College of Cornell University (O.B., L.M.R.).

Correspondence to Mario Barbagallo, MD, Professor of Medicine, Head of Geriatric Medicine, University of Palermo, Via F. Scaduto 6/c, 90144 Palermo Italy. E-mail mabar{at}unipa.it

Abstract

Abstract—— Previous studies by our group have identified ionic aspects of insulin resistance in hypertension, in which cellular responses to insulin were influenced by the basal intracellular ionic environment—the lower the cytosolic free magnesium (Mg_i), the less Mg_i increased following insulin stimulation. To investigate whether this ionic insulin resistance represents a more general abnormality of cellular responsiveness in hypertension, we studied Mg_i responses to nonhormonal signals such as hyperglycemia (15 mmol/L) and used ³¹P-nuclear magnetic resonance (NMR) spectroscopy to measure Mg_i in erythrocytes from normal (NL, n=14) and hypertensive (HTN, n=12) subjects before and 30, 60, 120, and 180 minutes after in vitro glucose incubations. Basal Mg_i levels were significantly lower in HTN subjects than in NL subjects (169±10 versus 205±8 µmol·L^-1, P<0.01). In NL cells, hyperglycemia significantly lowered Mg_i, from 205±8 µmol·L^-1 (basal, T=0) to 181±8, 162±6, 152±7, and 175±9 µmol·L^-1 (T=30, 60, 120, and 180, respectively; P<0.005 versus T=0 at all times). In HTN cells, maximal Mg_i responses to hyperglycemia were blunted, from 169±10 µmol·L^-1 (basal, T=0) to 170±11, 179±12, 181±14, and 173±15 µmol·L^-1 (T=30, 60, 120, and 180, respectively; P=NS versus T=0 at all times). For all subjects, Mg_i responses to hyperglycemia were closely related to basal Mg_i levels: the higher the Mg_i, the greater the response (n=26, r=0.620, P<0.001). Thus, (1) erythrocytes from hypertensive vis-à-vis normotensive subjects are resistant to the ionic effects of extracellular hyperglycemia on Mg_i levels, and (2) cellular ionic responses to glucose depend on the basal Mg_i environment. Altogether, these data support a role for altered extracellular glucose levels in regulating cellular magnesium metabolism and also suggest the importance of ionic factors in determining cellular responsiveness to nonhormonal as well as hormonal signals.

Key Words: magnesium • hyperglycemia • glucose • diabetes • magnetic resonance spectroscopy

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