Glucose-induced alterations of cytosolic free calcium in cultured rat tail artery vascular smooth muscle cells

We have previously suggested that hyperglycemia per se may contribute to diabetic hypertensive and vascular disease by altering cellular ion content. To more directly investigate the potential role of glucose in this process, we measured cytosolic free calcium in primary cultures of vascular smooth muscle cells isolated from Sprague-Dawley rat tail artery before and after incubation with 5 (basal), 10, 15, and 20 mM glucose. Glucose significantly elevated cytosolic free calcium in a dose- and time-dependent manner, from 110.0 +/- 5.4 to 124.5 +/- 9.0, 192.7 +/- 20.4, and 228.4 +/- 21.9 nM at 5, 10, 15, and 20 mM glucose concentrations, respectively. This glucose-induced cytosolic free calci…

Effects of Aging on Serum Ionized and Cytosolic Free Calcium

Abstract —Elevated cytosolic free calcium (Ca i ) and reciprocally reduced, extracellular ionized calcium (Ca-ion) levels are observed in both hypertension and non–insulin-dependent diabetes mellitus (NIDDM). Because the changes of vascular function and insulin sensitivity in these conditions resemble the changes associated with “normal” aging, we wondered to what extent similar alterations in calcium metabolism occur with aging per se in the absence of overt hypertension or diabetes. We therefore measured platelet Ca i levels by spectrofluorometry and serum Ca-ion levels in normotensive, nondiabetic, healthy, normal, elderly (>65 years old) subjects, mean age ±SEM, 72.2±1.5 years old (…

Vascular effects of progesterone: Role of cellular calcium regulation

Abstract —Vascular actions of progesterone have been reported, independently of estrogen, affecting both blood pressure and other aspects of the cardiovascular system. To study possible mechanisms underlying these effects, we examined the effects of P in vivo in intact rats and in vitro in isolated artery and vascular smooth muscle cell preparations. In anesthetized Sprague-Dawley rats , bolus intravenous injections of P (100 μg/kg) significantly decreased pressor responses to norepinephrine (0.3 μg/kg). In vitro, progesterone (10 −8 to 10 −5 mmol/L) produced a significant, dose-dependent relaxation of isolated helical strips, both of rat tail artery precontracted with KCl (60 mmol/L) or a…

Effects of Dehydroepiandrosterone Sulfate on Cellular Calcium Responsiveness and Vascular Contractility

Abstract Dehydroepiandrosterone sulfate (DHEAS) is an endogenous steroid having a wide variety of biological effects, but its physiological role remains undefined. Since an age-related decline of DHEAS corresponds to the progressive onset of atherosclerosis, cardiovascular diseases, and overall mortality, we investigated a possible protective role of DHEAS in vascular disease by studying the effects of this hormone (10 −7 to 10 −5 mol/L) on cytosolic free calcium and contractility in different in vitro vascular tissue preparations. DHEAS produced a significant, dose-dependent relaxation of isolated helical strips of rat tail artery precontracted with KCl (60 mmol/L) (89.7±18.7%, P <.01)…

Altered cellular magnesium responsiveness to hyperglycemia in hypertensive subjects.

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 31 P-nuclear magnetic resonance (NMR) spectroscopy to measure Mg i in erythrocytes from normal (NL, n=14) and hypertensive (HTN, n=12) subjects before and 3…

Magnesium metabolism in hypertension and type 2 diabetes mellitus.

The increasing evidence for the clinical relevance of altered magnesium metabolism to states of altered insulin resistance confirms the role of magnesium deficit as a possible underlying common mechanism of the "insulin resistance" of hypertension and altered glucose tolerance. The pioneer work of Lawrence M. Resnick and his group using the cellular ion-based approach that we are only partially presenting here has consistently contributed to the progress of the field, demonstrating (a) the critical importance of magnesium metabolism in regulating insulin sensitivity as well as vascular tone, and blood-pressure homeostasis; (b) that magnesium deficiency, defined on the basis of intracellular…

Effects of vitamin e and glutathione on glucose metabolism: Role of magnesium

Abstract —Vitamin E is an antioxidant that has been demonstrated to improve insulin action. Glutathione, another natural antioxidant, may also be important in blood pressure and glucose homeostasis, consistent with the involvement of free radicals in both essential hypertension and diabetes mellitus. Our group has recently suggested that the effects of reduced glutathione on glucose metabolism may be mediated, at least in part, by intracellular magnesium levels (Mg [i] ). Recent evidence suggests that vitamin E enhances glutathione levels and may play a protective role in magnesium deficiency–induced cardiac lesions. To directly investigate the effects of vitamin E supplementation on insul…

Altered cellular calcium responsiveness to insulin in normal and hypertensive pregnancy.

Objective To investigate the glucose-independent calcium-related effects of insulin from subjects with normal and hypertensive pregnancies. Method We used lndo-l fluorescence spectroscopy to measure cytosolic free calcium levels (Cai) in peripheral blood mononuclear cells (PBM) from 17 women (aged 20-40 years), six nonpregnant controls (NPC), five pregnant normotensive (PNT) women and six pregnant hypertensive (PHT) women, before and 5, 30, 60, 120 and 180 min after in vitro incubation with 200 microU/ml insulin. Results Basal Cai levels were significantly higher in PHT women (175.2 +/- 18.8 nmol/l) than they were in NPC women (122.8 +/- 2.8 nmol/l) and PNT women (123.9 +/- 3.5 nmol/l). The…

Effect of testosterone on intracellular Ca++ in vascular smooth muscle cells.

Effects of Glutathione on Red Blood Cell Intracellular Magnesium

Abstract —Recent evidence suggests that the endogenous antioxidant glutathione may play a protective role in cardiovascular disease. To directly investigate the role of glutathione in the regulation of glucose metabolism in hypertension, we studied the acute effects of in vivo infusions of this antioxidant (alone or in combination with insulin) on whole body glucose disposal (WBGD) using euglycemic glucose clamp and the effects on total red blood cell intracellular magnesium (RBC-Mg) in hypertensive (n=20) and normotensive (n=30) subjects. The relationships among WBGD, circulating reduced/oxidized glutathione (GSH/GSSG) levels, and RBC-Mg in both groups were evaluated. The in vitro effects…

Magnesium Responsiveness to Insulin and Insulin-Like Growth Factor I in Erythrocytes from Normotensive and Hypertensive Subjects

Depletion of intracellular free magnesium (Mg(i)) is a characteristic feature of insulin resistance in essential hypertension, but it is not clear to what extent low Mg(i) levels contribute to insulin resistance, result from it, or both. As insulin-like growth factor I (IGF-I) may improve insulin resistance, we investigated whether this peptide could similarly improve Mg(i) responsiveness to insulin in hypertension, and whether this effect was related to any direct IGF-I effect on Mg(i). 31P-Nuclear magnetic resonance spectroscopy was used to measure Mg(i) in erythrocytes from 13 fasting normotensive and 10 essential hypertensive subjects before and 30, 60, and 120 min after incubation with…

Cellular ionic alterations with age: relation to hypertension and diabetes.

BACKGROUND: Cytosolic free calcium (Cai) and magnesium (Mgi) are vital to cellular homeostasis and function. OBJECTIVE: To evaluate cellular divalent cations in normal subjects at different ages and their relationship to ion levels in essential hypertension and diabetes. DESIGN: A cross-sectional study. SETTING: A university hospital in New York. PARTICIPANTS: A total of 103 subjects (32 older, 71.1 ± 1.2 y/o, and 71 young/middle aged subjects, 51.1 ± 2.3 y/o). INTERVENTION: Oral glucose tolerance test. MEASUREMENTS: 19F and 31P NMR spectroscopy were used to measure Cai and Mgi levels in erythrocytes from normal (>65 y/o, n = 11; 65 y/o, n = 9; 65 y/o, n = 12; <65 y/o, n = 15) subjects; the…

Insulin-Mimetic Action of Vanadate

Abstract — — The insulin-mimetic effect of vanadate is well established, and vanadate has been shown to improve insulin sensitivity in diabetic rats and humans. Although the exact mechanism(s) remain undefined, we have previously demonstrated a direct relation of intracellular free magnesium (Mg i ) levels to glucose disposal, to insulinemic responses following glucose loading, and to insulin-induced ionic effects. To investigate whether the insulin-mimetic effects of vanadate could similarly be mediated by Mg i , we utilized 31 P-nuclear magnetic resonance spectroscopy to measure Mg i in erythrocytes from normal (NL, n=10) and hypertensive (HTN, n=12) subjects, before and after incubation…

Cellular-free magnesium depletion in brain and muscle of normal and preeclamptic pregnancy: A nuclear magnetic resonance spectroscopic study

Preeclampsia is a pregnancy disorder of unknown origin, characterized by vasospasm, elevated blood pressure, and increased neuromuscular irritability, features common to syndromes of magnesium deficiency. Evidence of serum and ionized magnesium metabolism disturbances have been observed in women with preeclampsia. This and the therapeutic utility of magnesium in preeclampsia led us to investigate the extent to which an endogenous tissue magnesium deficiency might be present in and contribute to its pathophysiology. We used 31 P nuclear magnetic resonance spectroscopy to noninvasively measure in situ intracellular-free magnesium levels in brain and skeletal muscle of fasting nonpregnant wom…

The Ionic Hypothesis of Aging

The clinical association of essential hypertension with metabolic abnormalities, such as hyperinsulinemia, insulin resistance, obesity, altered glucose tolerance and/or frank non-insulin dependent diabetes mellitus (NIDDM) has long been appreciated(1). Each of the above clinical conditions is extremely frequent in the elderly. The association of these different clinical states, that is also common at younger ages, has been termed “Syndrome X” and more recently “Generalized Cardiovascular-Metabolic Disease.”(2,3) Although several hypothesis have been proposed, including a primary role of hyperinsulinemia and insulin resistance, the mechanism(s) of this linkage has not been established. This …