The impact of vanadate on the Na,K-ATPase system in the vascular smooth muscle cell is poorly understood. The present study describes the kinetics of the effect of vanadate on Na,K-ATPase and the Na-K pump in in vitro grown rat VSMC's. Vanadate interaction with the Na,K-ATPase system in vascular smooth muscle cells was examined by observing its influence on ouabain-sensitive adenosine triphosphate hydrolysis in disrupted cells rendered permeable by osmotic shock, and the uptake of rubidium by intact cells. The I50 for vanadate inhibition of ouabain-sensitive hydrolysis of adenosine triphosphate occurred at vanadate concentrations of 10(-6) to 10(-7) M. This inhibition was potassium dependent. The maximal inhibitory effect of vanadate occurred at potassium concentrations of 10-20 mEq/liter. Sodium exerted a moderate antagonistic influence on vanadate inhibition of ouabain-sensitive adenosine triphosphate hydrolysis. Rubidium uptake by vascular smooth muscle cells was not altered within 120 minutes when 10(-5) M vanadate was added to the medium containing intact vascular smooth muscle cells. Yet, vanadium concentrations in the vascular smooth muscle cells within this incubation period reached levels 1.48-fold higher than the extracellular vanadate concentrations of 10(-5) M. These observations indicate that vanadate is a potent inhibitor of the VSMC Na,K-ATPase in disrupted vascular smooth muscle cells. However, in intact vascular smooth muscle cells vanadium gaining access into the vascular smooth muscle cell's interior does not inhibit the Na-K pump, probably because of its binding to intracellular proteins and/or conversion from the vanadate to the vanadyl ion.

Forty-six female Sprague-Dawley rats (170-200 g) were randomly assigned to one of six treatment groups receiving 0.1, 5.0, or 25.0 ppm dietary vanadium with either normal (0.13 mEq/g) or high (1.82 mEq/g) dietary potassium. Supplemental vanadium was administered as sodium metavanadate. These diets were fed for 2 weeks, and all feces and urine collected. At the end of the treatment period, brain, liver, renal cortex and medulla, whole blood, and plasma were obtained and analyzed for vanadium by atomic absorption spectrophotometry, as were the urine and feces samples. Tissue vanadium concentration increased significantly (P less than 0.00001) with increasing food vanadium content, but were not affected by dietary potassium in spite of the polyuria induced in animals on the high potassium diets. The highest vanadium concentrations were found in the renal cortex and the lowest, in the brain. Although urinary vanadium excretion was higher in animals fed the high potassium diets, a relatively small percentage of ingested vanadium was excreted in the urine. Rats fed diets containing no supplemental sodium metavanadate (0.1 ppm vanadium) were in negative vanadium balance, but their growth was not inhibited. Animals receiving 5.0 and 25.0 ppm vanadium diets retained 39.7 +/- 18.5% of ingested vanadium and excreted 59.1 +/- 18.8% of ingested vanadium in the feces. These values indicate greater absorption and retention of ingested vanadium than found In previously reported investigations.

Many epidemiologic studies have disclosed that restricted fetal growth has been associated with an increased risk of insulin resistance in adulthood. We studied the relationship of intracellular magnesium ([Mg 2ϩ ] i ) in cord blood platelets to adipocytokine and birth size. The subjects were 20 infants with small for gestational age (SGA) and 45 infants with appropriate for gestational age (AGA). By using a fluorescent probe, we examined [Mg 2ϩ ] i of platelets in the cord blood. Cord plasma insulin, IGF-I, ghrelin, adiponectin, plasminogen activator inhibitor-1 (PAI-1), and leptin levels were determined with the use of ELISA. Mean [Mg 2ϩ ] i was lower in the SGA than in the AGA groups (p Ͻ 0.001). Adiponectin and IGF-I were also lower in the SGA than in the AGA, whereas PAI-1 was higher in the SGA. [Mg 2ϩ ] i was significantly correlated with birth weight, birth length, and adiponectin. Birth weight was also correlated with cord plasma IGF-I, adiponectin, and leptin. Quantitative insulin sensitivity check index (QUICKI) was lower in the SGA group than in the AGA group. T here is no doubt that low birth weight is associated with adult disorders characterized by insulin resistance such as type 2 diabetes, hypertension, dyslipidemia, and coronary heart disease (1,2). It has been proposed that this association results from fetal programming in response to the intrauterine environment (3). Intracellular magnesium (Mg 2ϩ ) i deficiency occurs in patients with diabetes and vascular diseases (4 -6). Taken together, these experimental and epidemiologic results suggest that the correlation between Mg 2ϩ and birth weight are important determinants of insulin resistance. We and other investigators reported that insulin could regulate intracellular Mg 2ϩ ([Mg 2ϩ ] i ) in platelets (7,8). Platelets are often used in the study of cellular cation metabolism in diseases (9), because they are readily available for study and are thought to share a number of features with vascular smooth muscle cells. Human platelets have been shown to have insulin receptors with similar characteristics as those in other cells (10 ] i and birth weight (11). As the next step, we hypothesized that [Mg 2ϩ ] i may affect metabolic hormones and insulin resistance in infants. We studied the correlation among [Mg 2ϩ ] i , adipokines in cord blood and insulin resistance index. SUBJECTS AND METHODSThe study group consisted of 65 singleton subjects with gestational ages ranging from 33 to 41 wk, and birth weights ranging from 1332 to 4030 g. Most of these subjects had been previously recruited for an observational study of [Mg 2ϩ ] i (11). Gestational age was measured by dating the last menstrual period at the time of registration. None of the subjects were treated with medications, including magnesium, and did not show any evidence of endocrine malfunction or recent use of drugs that might potentially alter electrolyte balance. All the mothers were Japanese with no remarkable past medical histories, and they manifested no abno...

This study has focused on the characteristics of the Na+-K+-ATPase in in vitro preparations of vascular smooth muscle cells (VSMCs) derived from the rat carotid artery. The maximum velocity of enzyme reaction (Vmax) for the specific activity of the enzyme in the VSMCs' preparations was 2.36 +/- 0.04 (SE) mumol Pi X mg cell protein-1 X h-1 or 0.82 +/- 0.02 mumol Pi X 10(6) cells-1 X h-1. The activation of the enzyme by potassium, sodium and ATP has been investigated. The half-maximal values for potassium and sodium activation of the enzyme in the preparations were 1.18 and 10-20 meq/l, respectively. The respective Vmax values for potassium and sodium activation were reached at concentrations of 4-10 and 80-100 meq/l. The Michaelis constant for ATP was 0.83 mM. Calcium exerted a potent inhibition on the activity of the enzyme (I50 at 1 mM). It has been concluded that the Na+-K+-ATPase kinetic pattern in in vitro preparations of VSMCs is quite similar to that observed in homogenates or subcellular fractions of other tissues.