Na+ concentrations

The volume of extracellular fluid is direcdy related to the Na" concentration which is closely controlled by the kidneys. Homeostatic control of Na" concentration depends on the hormone aldosterone. The kidney secretes a proteolytic enzyme, rennin, which is essential in the first of a series of reactions leading to aldosterone. In response to a decrease in plasma volume and Na" concentration, the secretion of rennin stimulates the production of aldosterone resulting in increased sodium retention and increased volume of extracellular fluid (51,55). 

In general, cells maintain a low inttaceUulat Na concentration and a high intracellular K+ concentration (Table 41-1), along with a net negative electrical potential inside. The pump that maintains these gradients is an ATPase that is activated by Na and (Na -K ATPase see Figure 41-13). The ATPase is an integral... 

PTX caused a dose-dependent release of norepinephrine (NE). The NE release induced by lower concentrations of PTX increased proportionately with increasing Na concentrations, but was not modified by tetrodotoxin. However, the NE-releasing action of higher concentrations of PTX was dependent on external Ca, but not Na . Thus our experimental results suggest that in adrenergic neurons the PTX-induced release of NE by lower concentrations of PTX is brought about by tetrodotoxin-insensitive Na permeability, whereas that induced by higher concentrations is mainly caused by a direct increase of Ca influx into smooth muscle cells. 

Several other conditions can provoke this reverse pump type of release. One is when the transmembrane ionic gradient is reversed. Experimentally this is achieved by reducing extracellular Na+. Because the neuronal uptake of monoamines from the synapse by the transporter requires co-transport of Na+ and Cl , reversing the ionic gradient (so that the Na+ concentration is lower outside, than inside, the terminals) will drive the transporter in the wrong direction. Such carrier-mediated release could explain the massive Ca +-independent release of noradrenaline during ischaemia which increases intracellular Na+ concentration and reduces intracellular K+. 

It has been long believed that a lithium ion-selective electrode would render obsolete the flame photometer in the clinical laboratory. Lithium is administered to manic depressive psychiatric patients. Since the therapeutic range (0.5-1.5 mM) is quite close to the toxic range (>2 mM), it must be closely monitored. Most of the iono-phores propo d to date have not met the Li" /Na selectivity required for an interference-free assay. However, it has been reported that calibration in the presence of 140 mMNa permitted the analysis of Li in serum The errors observed are due to fluctuations in the Na concentrations in the sample. More selective ionophores would certainly improve the accuracy of this method. 

Figure 1.86. Variation in chemical compositions (in molal unit) of hydrothermal solution with temperature. Thermochemical data used for the calculations are from Helgeson (1969). Calculation method is given in Shikazono (1978a). Chloride concentration in hydrothermal solution is assumed to be 1 mol/kg H2O. A-B Na concentration in solution in equilibrium with low albite and adularia, C-D K concentration in solution in equilibrium with low albite and adularia, E-F HaSiOa concentration in equilibrium with quartz, G-H Ca + concentration in equilibrium with albite and anorthite (Shikazono, 1978a, 1988b).

FIG. 6 Time-course changes of potential response for silicone-rubber-membrane Na+-selective electrodes based on neutral carriers (5), (2), and bis(12-crown-4) on changing Na concentration from 1 X 10 to 3 X 10 M. (From Ref. 22.)... 

Applicability in biological ion assay is an important factor for biocompatible potentio-metric ion sensors. Attempts were made to determine Na" " concentrations in human blood sera by using silicone-rubber membrane Na+-ISFETs based on (5) [Fig. 17(a)] [29]. The found values for Na concentration in undiluted, 10-fold diluted, and 100-fold diluted serum samples are in good agreement with the Na" " calibration plots. Even in the undiluted serum samples, only a slight potential shift was observed from the calibration. This indicates that the calixarene-based silicone-rubber-membrane Na+-ISFETs are reliable on serum Na assay. For comparison with the silicone-rubber membrane, Na -ISFETs with corresponding plasticized-PVC membrane containing (2) or (5) were also tested for the Na assay. The found values of Na" " concentration... 

The Na -selective electrodes based on silicone-rubber membranes modified chemically by (8) and (9), were also investigated for Na assay in control serum and urine [22]. The found values for the Na concentrations in both of the serum and urine samples are in good agreement with their corresponding actual values with a relative standard deviation of about 1%. These results suggest that the Na -selective electrodes based on silicone-rubber membranes modified chemically by calix[4]arene neutral carrier (8) are reliable on assay in human body fluid. 

FIG. 18 Correlation between actual and found values of Na+ concentrations on serum assay with ISFETs based on sol-gel-derived membranes of bis(12-crown-4) (11). (From Ref. 49.)... 

Sodium deficit (mEq) = (TBW)(desired Na+ concentration -current Na+ concentration)... 

Hyponatraemia A lower-than-normal blood Na+ concentration. 

Na+ concentrations confirms their common marine origin. However, the concentration variations with depth are much less clear than the sinusoidal oscillations at J-9. At Station Q-13, only 70 km... 

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