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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Salts of sulfate, lithium, and bromine were injected or infused intravenously into ewes in the last trimester of gestation. Ewes and fetuses had indwelling catheters; most fetuses were nephrectomized. Concentrations were measured in paired maternal and fetal samples over periods of 4--14 days. Maternal excretion of sulfate was too rapid to permit near equilibration of fetal and maternal plasma concentrations; the results, however, did not support the existence of a large potential difference across the exchange barrier. The concentrations of Li+ (given by continuous infusion) and 82Br- in maternal plasma did not change rapidly. The concentrations of these tracers in fetal plasma rose until they were nearly equal to the maternal plasma concentrations. Steady-state transplacental potentials, calculated by use of the Nernst equation, were 5.2 +/- 2.0 (SEM) mV (n = 26) for Li+ and -2.2 +/- 0.8 (SEM) mV (n = 10) for Br-. Nernst potentials calculated from previously measured maternal and fetal plasma concentrations of Na+, K+, Mg2+, and Cl- were +0.4, +3.6, +0.5, and -1.4 mV. We concluded that, of the total potential difference of about -50 mV (fetus negative) between the fetal lamb and the ewe, only a few mV are dropped across the placental exchange barrier.
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PMID:Distribution of ionic sulfate, lithium, and bromide across the sheep placenta. 43 39

The magnesium status of 185 moderate income American mothers was assessed in the immediate postpartum period by the intravenous magnesium load test. Pre- and postload collections of urine were each made for approximately 24 hours because pilot studies revealed significant diurnal variation in magnesium excretion. The magnesium load provided 0.4 to 0.5 mEq of magnesium/kg of estimated lean body weight. The mean retention was 51% +/- 2.2 (SEM). Patients retaining more or less than an arbitrary limit of 40% of the magnesium load were compared. No differences in mean age, weight, or parity were found between the groups. The high retention group reported a diet lower in magnesium and had a significantly lower plasma magnesium value. Magnesium retention of over 90% of the load was found in biologically immature multiparas (less than 17 years) and in young mothers of twins. Among the multiparous patients, those with the longest interval since the previous pregnancy had the lowest retention values. Most of the primiparous patients had met the magnesium requirements of a singleton pregnancy and rejected most of the load, but 6 primiparous women whose active labor exceeded 18 hours had a retention of 77.91% of the load. This was significantly higher than the 45.0 +/- 3.52 (SEM) % retention in 70 primiparous mothers with shorter duration of active labor (P less than 0.005). No other symptoms or complications of pregnancy could be correlated with the magnesium load values. Further definition of the magnesium load test is indicated.
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PMID:Parenteral magnesium load tests in postpartum American women. 118 Feb 45

We have investigated the direct effects of different neuroexcitatory amino acids (EAA) on the secretion of CRH-41 and arginine vasopressin (AVP) from the rat hypothalamus maintained in vitro. CRH-41 and AVP released in the medium were assayed by RIA before and after incubation with N-methyl-D-aspartate (NMDA), N-methyl-D,L-aspartic acid, kainate (KA), and quisqualate in the concentration range 1 nM to 1 mM in either the absence or the presence of 1 mM Mg2+ in the medium. In the case of NMDA, the effect of the addition of glycine (1 and 10 microM) to the incubation medium was also studied. Finally, we investigated whether different periods of exposure (up to 100 min) of hypothalamic explants to NMDA and KA would affect CRH-41 release. While no EAA was able to induce CRH-41 release under any of the above conditions, 20-min incubations with NMDA in the dose range of 1 nM to 1 mM in the absence of added Mg2+ significantly stimulated AVP release in a dose-related fashion; the maximum effect occurred at a concentration of 1 mM [ratio of stimulated collection/basal collection: NMDA, 1.51 +/- 0.10, controls, 0.86 +/- 0.05 (mean +/- SEM); P < 0.001]. KA also showed a dose-related stimulatory effect in the dose range of 1 nM to 1 mM, with maximal AVP stimulation at 10 microM (KA, 1.91 +/- 0.28; controls, 0.90 +/- 0.03; P < 0.01). The effects of both NMDA and KA on AVP were completely reversed by the competitive antagonists D,L-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3 dione, respectively, at doses 10 times higher than those of the agonists. N-Methyl-D,L-aspartic acid stimulated AVP secretion only at a dose of 10 mM (P < 0.01), whereas quisqualate was ineffective at any concentration. The addition of 1 mM Mg2+ to the medium blocked the effect of NMDA, while attenuating AVP stimulation induced by KA. The stimulatory effect of KA on AVP was significantly reduced by D-L-2-amino-5-phosphonovaleric acid (P < 0.05), suggesting that KA may also act through NMDA receptors. Moreover, the presence of glycine in the incubation medium did not result in any effect of NMDA on CRH-41 secretion, nor did it appear to potentiate NMDA-induced AVP release.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Differential effects of neuroexcitatory amino acids on corticotropin-releasing hormone-41 and vasopressin release from rat hypothalamic explants. 135 61

Cerebrospinal fluid and serum were obtained from 16 clinically normal adult cows (11 dairy, 5 beef). Sodium, potassium, magnesium, total protein, and albumin concentrations, osmolality, and lactate dehydrogenase and creatine kinase activities, were quantified in CSF and serum. Total and differential cell counting, protein electrophoresis, and IgG quantification were performed on CSF. Statistical analyses of these variables, including mean, SEM, range, and 95% confidence intervals, were performed. Effects of blood contamination were evaluated, and were found to be negligible for all measured constituents. Correction factors for CSF creatine kinase and lactate dehydrogenase activities accounting for cellular contamination were developed. Total nucleated cell count was similar to counts in CSF of other species, but higher than values in healthy people. Differential leukocyte count in CSF was similar to that reported in CSF of other domestic animals: mostly lymphocytes, fewer monocytoid cells, and scant neutrophils. Cerebrospinal fluid protein concentration was higher than concentration reported for dogs, goats, and people, but was similar to values reported for horses. Beef cows had higher CSF total protein concentration than did dairy cows; also, beef cows had higher CSF gamma-globulin concentration. The concentration of sodium in CSF was slightly higher than the value in serum, and potassium concentration was lower than the value in serum. In contrast to studies of human beings, CSF osmolality was generally less than serum osmolality in the cows studied. Reference values for CSF electrolyte concentrations and osmolality are useful for diagnosis of salt poisoning and for assessment of the effects of fluid therapy. Magnesium concentration was lower in CSF, compared with serum.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Composition and analysis of cerebrospinal fluid in clinically normal adult cattle. 146 1

Skeletal muscle temperature and mitochondrial content of Ca2+ and Mg2+ were measured after 3 h of total or partial limb ischemia in male Wistar rats (250-350 g). The decreases in biceps muscle temperature, measured with a needle thermistor (4.4 +/- 0.26 degrees C, mean +/- SEM (17 rats) and 6.3 +/- 0.26 degrees C (31 rats) in partial ischemia (PI, aorta clamp) and total ischemia (TI, hind leg tourniquet), respectively) were consistent with the expected extent of blood flow reduction for the two ischemic conditions. Mitochondrial calcium levels increased after partial ischemia from 2.67 +/- 0.13 (46 rats) to 4.65 +/- 0.38 (12 rats) nmol/mg protein and increased to 7.87 +/- 0.68 (14 rats) after total ischemia (P less than 0.05). In contrast, mitochondrial magnesium decreased after partial ischemia from 10.14 +/- 0.35 to 8.22 +/- 0.28 (13 rats) but increased in the mitochondria of muscle submitted to total ischemia to 12.0 +/- 0.80 (14 rats; P less than 0.05). No changes were observed in the number of binding sites for safranine, which competes for calcium binding sites on the inner mitochondrial membrane (25.46 +/- 0.38 nmol/mg protein for sham (20 rats) and 25 +/- 0.68 (7 rats) for PI and 25 +/- 0.31 (5 rats) for TI). The data suggest that the greater resistance of rat muscle to total than to partial ischemia may be due at least in part to the increased mitochondrial Mg2+ content.
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PMID:Intramitochondrial calcium and magnesium levels in skeletal muscle submitted to total or partial limb ischemia. 182 2

The effects of metabolic (bicarbonate, [HCO3]) and respiratory (carbon dioxide, PCO2) acid-base changes on indirectly elicited twitch tension with and without nondepolarizing neuromuscular blocking agents were compared in a rat phrenic nerve-hemidiaphragm preparation. Ionized calcium [Ca2+] and magnesium [Mg2+] concentrations in the modified Krebs' solution were measured and kept constant. Likewise, twitch was altered when pH changes were produced by altering either PCO2 or [HCO3]. Decreasing pH either by increasing PCO2 or by decreasing [HCO3] significantly decreased (P less than 0.01) twitch, by 9.5 +/- 0.6 (SEM, n = 8) and 10.6 +/- 1.5%, respectively. Increasing pH by decreasing PCO2 or by increasing [HCO3] significantly increased (P less than 0.01) twitch, by 5.6 +/- 0.9 and 7.9 +/- 0.6%, respectively. After a partial depression of twitch by nondepolarizing neuromuscular blocking agents, the effects of PCO2 and [HCO3] changes were again assessed. Decreasing pH by increasing PCO2 or by decreasing [HCO3] intensified d-tubocurarine (dTc) (28.2 +/- 1.6 and 32.0 +/- 2.9%, respectively) and vecuronium (23.0 +/- 1.4 and 36.8 +/- 3.2%, respectively) block, whereas it reversed metocurine (1.2 +/- 2.2% NS and 2.9 +/- 1.3%, respectively) and pancuronium (8.3 +/- 1.5 and 11.5 +/- 3.0%, respectively) block. Conversely, increasing pH by decreasing PCO2 or by increasing [HCO3] antagonised dTc (12.8 +/- 2.2 and 13.6 +/- 1.8%, respectively) and vecuronium (25.3 +/- 1.7 and 25.0 +/- 3.0%, respectively) block, whereas it potentiated metocurine (4.2 +/- 0.6 and 8.0 +/- 1.1%, respectively) and pancuronium (11.0 +/- 1.2 and 17.5 +/- 2.0%, respectively) block. Except where indicated, all changes in block described above were statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Neuromuscular effects of respiratory and metabolic acid-base changes in vitro with and without nondepolarizing muscle relaxants. 153 Dec 87

Honey bee photoreceptors contain large sacs of endoplasmic reticulum (ER) that can be located unequivocally in freeze-dried cryosections. The elemental composition of the ER was determined by electron probe x-ray microanalysis and was visualized in high-resolution x-ray maps. In the ER of dark-adapted photoreceptors, the Ca concentration was 47.5 +/- 1.1 mmol/kg (dry weight) (mean +/- SEM). During a 3-sec nonsaturating light stimulus, approximately 50% of the Ca content was released from the ER. Light stimulation also caused a highly significant increase in the Mg content of the ER; the ratio of Mg uptake to Ca released was approximately 0.7. Our results show unambiguously that the ER is the source of Ca2+ release during cell stimulation and suggest that Mg2+ can nearly balance the charge movement of Ca2+.
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PMID:Electron probe microanalysis of calcium release and magnesium uptake by endoplasmic reticulum in bee photoreceptors. 199 66

To determine intracellular Ca2+ concentrations more accurately, we examined Kd of Fura-2 for Ca2+ in conditions which were systemically changed. In a solution comprising of 150 mM KCI, 20 mM MOPS-KOH, pH 6.94, 60-100 microM EGTA and 1 microM Fura-2, Kd at 20 degrees C was 0.266 +/- 0.016 microM (mean +/- SEM) (21 determinations). The ionic strength (I) of the solution strongly affected Kd: the relation of -log Kd versus 2 square root of I/(1 + square root of I) - 0.4.I was 3.6 times as steep as that of EGTA. Kd was moderately changed by pH higher than 7.1, while it was very slightly changed by pH between 6.7 and 7.1. Kd was minimally affected by temperature. The apparent Kd values for Ca2+ in the presence of various concentrations of Mg2+ gave an estimate of the Kd for Mg2+ of about 100 mM, which is about 10 times as great as the estimated value by Grynkiewicz et al. [1]. This estimation assumes competitive binding between Ca2+ and Mg2+ for Fura-2. However, the possibility that Mg2+ may bind Fura-2 in a more complicated way is also suggested. Co-existing proteins in the solution dose-dependently increased an apparent Kd, independent of the type of proteins used, up to a limiting value of about 1.0 microM. With the ratio method, the Ca2+ concentration which gives (Rmin + Rmax)/2 is Kd.beta. The range of Ca2+ concentrations on which R values show steep dependence is determined not only by Kd but also by beta. This means that the excitation spectra and pair of excitation wavelengths selected as well as Kd are critical factors.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Reassessment of Fura-2 and the ratio method for determination of intracellular Ca2+ concentrations. 201 20

Furaptra (Raju, B., E. Murphy, L. A. Levy, R. D. Hall, and R. E. London. 1989. Am. J. Physiol. 256:C540-C548) is a "tri-carboxylate" fluorescent indicator with a chromophore group similar to that of fura-2 (Grynkiewicz, G., M. Poenie, and R. Y. Tsien. 1985. J. Biol. Chem. 260:3440-3450). In vitro calibrations indicate that furaptra reacts with Ca2+ and Mg2+ with 1:1 stoichiometry, with dissociation constants of 44 microM and 5.3 mM, respectively (16-17 degrees C; ionic strength, 0.15 M; pH, 7.0). Thus, in a frog skeletal muscle fiber stimulated electrically, the indicator is expected to respond to the change in myoplasmic free [Ca2+] (delta[Ca2+]) with little interference from changes in myoplasmic free [Mg2+]. The apparent longitudinal diffusion constant of furaptra in myoplasm was found to be 0.68 (+/- 0.02, SEM) x 10(-6) cm2 s-1 (16-16.5 degrees C), a value which suggests that about half of the indicator was bound to myoplasmic constituents of large molecular weight. Muscle membranes (surface and/or transverse-tubular) appear to have some permeability to furaptra, as the total quantity of indicator contained within a fiber decreased after injection; the average time constant of the loss was 302 (+/- 145, SEM) min. In fibers containing less than 0.5 mM furaptra and stimulated by a single action potential, the calibrated peak value of delta[Ca2+] averaged 5.1 (+/- 0.3, SEM) microM. This value is about half that reported in the preceding paper (9.4 microM; Konishi, M., and S. M. Baylor. 1991. J. Gen. Physiol. 97:245-270) for fibers injected with purpurate-diacetic acid (PDAA). The latter difference may be explained, at least in part, by the likelihood that the effective dissociation constant of furaptra for Ca2+ is larger in vivo than in vitro, owing to the binding of the indicator to myoplasmic constituents. The time course of furaptra's delta[Ca2+], with average values (+/- SEM) for time to peak and half-width of 6.3 (+/- 0.1) and 9.5 (+/- 0.4) ms, respectively, is very similar to that of delta[Ca2+] recorded with PDAA. Since furaptra's delta[Ca2+] can be recorded at a single excitation wavelength (e.g., 420 nm) with little interference from fiber intrinsic changes, movement artifacts, or delta[Mg2+], furaptra represents a useful myoplasmic Ca2+ indicator, with properties complementary to those of other available indicators.
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PMID:Myoplasmic calcium transients in intact frog skeletal muscle fibers monitored with the fluorescent indicator furaptra. 201 81

It is now well established that the pathophysiology of the malignant hyperthermia (MH) syndrome is related to a malfunction of intracellular calcium homeostasis. Magnesium plays important roles in the basic contractile properties of muscle, and many of its actions are antagonistic to those of calcium. The aim of this study was to determine the effectiveness of magnesium sulphate to prevent the MH episode in susceptible animals and correlate this with its effects on the intracellular free calcium [( Ca2+]i). The experiments were carried out using six control (Yorkshire) and ten MH-susceptible crossbred swine (Poland China X Pietrain). After determination of resting concentrations of [Ca2+]i and [Mg2+]i, each animal was given either two iv bolus doses of 50 mg/kg or one iv bolus of 100 mg/kg of MgSO4. The resting [Ca2+]i and [Mg2+]i were determined by means of ion-selective microelectrodes. The resting [Ca2+]i in normal muscle fibers was 0.11 +/- 0.01 microM (mean +/- SEM), whereas in the MH muscles the resting [Ca2+]i was 0.36 +/- 0.01 microM. In neither group was the resting [Ca2+]i modified by MgSO4. This cumulative dose of MgSO4 (100 mg/kg) was not able to prevent the induction of an MH episode by 2% halothane. Although MgSO4 did not directly decrease [Ca2+]i, it did attenuate the increase in [Ca2+]i associated with the syndrome from 7.29 +/- 0.43 microM in untreated animals to 0.84 +/- 0.03 microM in MgSO4 pretreated swine. In addition, the limb rigidity that accompanies this increase in calcium was prevented by MgSO4 pretreatment. Baseline measurements of [Mg2+]i were not different in control and MH-susceptible muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The effects of extracellular magnesium on myoplasmic [Ca2+] in malignant hyperthermia susceptible swine. 236 Jul 20


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