Physiological chemistry and physics最新文献

A transient time is needed for a potential step to travel through the solution between the metal electrode and the membrane. The effects of the double layer that exists at the electrode-solution interface may cause a delay for the signal reaching the surface of the membrane to initiate any voltage dependent reaction. The process by which the ions of the solution redistribute themselves is described by a relaxation model. The relaxation time is related to the resistance of the solution and the equivalent capacitance of the diffuse double layer. The theory is then applied to the experiments that measured the gating process of nerve membrane. The delay time of the rise in the sodium conductance on polarization is calculated for various polarized potentials and holding potentials and the numerical results can explain the experimental data without using the multi-state kinetic models. It indicates that the relaxation time of the solution should be taken into consideration for any membrane experiment with time courses of similar order.

Ovarian and body cavity eggs from R. temporaria were exposed to radiofrequency (rf) electromagnetic fields in the frequency range 10-27 MHz with specific absorption rates (SAR) up to 800 W/kg. The effect of the exposure was investigated by measurement of the water-related cell physiological parameters, isotopic and osmotic water membrane permeability and density of the egg cells. Only the osmotic water permeability, Pf, of ovarian eggs was significantly altered. A decrease of about 30% was seen for SARs of 50 W/kg and exposure times up to 2 h. Tests ruled out that the effect was due to temperature increase during the exposure. The observed decrease of Pf was most likely due to cloudy swelling of the egg cytoplasm resulting from the rf irradiation.

Isopiestic data indicate that glycogen appreciably reduces the osmotic and activity coefficients of potassium phosphates relative to those of the corresponding sodium salts. Dimethylurea has a similar but smaller effect. This reduction of osmotic coefficients is probably due either to (1) the lesser ability of potassium ion, relative to sodium ion, to compete for water of hydration with the hydrophilic glycogen and a resultant stronger ion pairing of the potassium and phosphate ions; or to (2) the formation of a weak potassium-glycogen-phosphate complex. This behavior offers an explanation for the correlation between cellular glycogen and potassium.

Clinical study has shown that high-potassium in addition to low-sodium diet therapy for human cardiac disease is much more effective than low-sodium diet alone or than the usual drug therapies. Analyzed by the association-induction concept of adsorbed cellular sodium and potassium, the clinically measured changes of blood sodium and potassium due to the combined diet would be expected to yield marked improvement in intracellular sodium and potassium because of the nonlinear shape of the expected cation adsorption curves. Indicated is a significant approach toward restoring normality of the intracellular cationic environment in cardiac patients.

The mechanism of the in vitro PGBx effect on mitochondria was studied by determining the specific requirements of the assay system composition. These studies showed that (a) rat liver mitochondria must first be exposed to hypotonic media containing PGBx under aerobic conditions, (b) oxygen, Pi, Mg++, phosphate acceptor (nucleotides), and some oxidizable substrates are essential components to yield optimal phosphorylation values. KCl and bovine serum albumin are non-essential components. With regard to nucleotide acceptor specificity, the AMP, ADP, and glucose-ADP-hexokinase systems were satisfactory. With regard to substrate specificity, only beta-hydroxybutyrate and externally reduced NAD+ were unsatisfactory. The requirement for oxygen was twofold: (a) as an absolute requirement for oxidative phosphorylation, and (b) as a requirement for the hypotonic degradation of mitochondria. These results suggest that PGBx reacts with mitochondria to "protect" against degradation during aerobic hypotonic exposure.

A relatively simple procedure for the measurement of urinary chemiluminescence is described and some of the variables affecting such measurements are examined. Normal urinary chemiluminescence is due to lipoperoxidation, presumably through the Haber-Weiss reaction, generating singlet oxygen as emitter. It was found that urinary chemiluminescence was higher in normal smokers than in normal non-smokers and very low in cancer patients. Oral distribution of ascorbic acid reduced urinary chemiluminescence of both normal smokers and non-smokers. Presumably, the spontaneous chemiluminescence in the urine could serve as a cancer marker.

The effect of 1-propanol, 2-propanol, n-butanol, ethanol and methanol an sorbitol dehydrogenase activity was assayed. The inhibition type was also investigated and results obtained are reported.

Since prostaglandin E2 is generally stimulatory to intestinal and nonparietal gastric secretions, possible stimulation of parietal gastric acid secretion was investigated. Oxygen consumption of parietal cells isolated from rat stomach was determined before and after addition of 16,16-dimethyl prostaglandin E2 (dmPGE2). At low concentration, dmPGE2 significantly stimulated oxygen consumption of parietal cells by 7%. Concomitantly, acid secretion rose. H+ transport in the isolated gastric mucosa of the rat was determined in the absence of electrochemical gradients to preclude H+ back-diffusion. Compared with control rates, H+ transport from submucosal to mucosal side was stimulated 51% by the same low concentration of dmPGE2. It is concluded that stimulation of gastric acid secretion by parietal cells appears to be a physiological function of prostaglandin E2 in the stomach. The results support the hypothesis that prostaglandins stimulate secretory responses throughout the gastrointestinal tract.

Measurements are reported of NMR relaxation times (T2) on hydrogen in water of isotonic NaCl solutions and of normal human amniotic fluid in which known concentrations of meconium (fetal feces) were dissolved. Magnetic fields for resonance of 23.5 X 10(3) and 0.6 oersteds were used. From the measured T2 values, reliable estimates of meconium concentrations could be obtained that might be considered estimates of fetal distress. Observed minor variation of T2 values was probably due to the mucopolysaccharides comprising 80% of the meconium weight. Advantages of this technique for possible clinical use in obstetrics include small volume of sample required (0.1 ml), lack of necessity for sample filtration or centrifugation, and shortness of time required for analysis (less than 30 min).