Localization and characterization of sodium transport along the renal tubule

The proximal tubular Na transport system was investigated using our stop flow analysis. During varying degrees of osmotic diuresis in dogs the ureter of one kidney was occluded for 2 1/2–8 minutes. Following occlusion serial urine samples were collected and analyzed for Na, creatinine, PAH or glucose. Using urinary creatinine concentrations as an index of water movement the mass of Na and water reabsorbed from the proximal segments during occlusion was calculated. In all experiments the calculations showed that the Na concentration in the proximal reabsorbate was of the same concentration which existed in plasma. Such behavior is inconsistent with a proximal Na pump which would otherwise reabsorb a supraplasma-level Na solution away from mannitol and Na in the tubule. The data suggest that Na and water transport out of the proximal tubules may be a passive process initiated by the colloidal osmotic pressure differences which exist between the intratubular urine and the peritubular capillary blood. A passive mechanism for Na and water reabsorption from the proximal segment resolves many difficulties faced by a Na pump.

Apparent sodium space of the dog

After the intravenous injection of 2 gm/kg of sodium chloride in 20% solution in dogs whose total urine output was reinfused intravenously, sodium spaces were found to be 80 ± 2.8% of total body weight. The chloride space was found to be 58 ± 1.6% of the total body weight. Urine flow increased markedly. Plasma potassium concentration fell. The large sodium space was thought to be due to large total body water spaces in our animals or to the presence of a nonaqueous sodium space.

Sodium and potassium binding by rat liver cell microsomes

The effects of ion concentration, pH, and presence of competing ions on the sodium and potassium binding properties of rat liver cell microsomes were studied. Typical adsorption isotherms were obtained in the concentration dependence studies, with saturation being reached when 1.2 to 1.4 m.eq. cations were retained per gm. of microsome Kjeldahl nitrogen. The retention was shown to be due to a binding to specific sites rather than to a trapping of the cations. The binding showed a sharp pH dependence in the range 6.0 to 7.5. The presence of one cation depressed the binding of the other, indicating that Na⁺ and K⁺ as well as H⁺ ions compete for the same sites. Potassium was bound slightly more strongly than sodium, while hydrogen was bound about 10⁵ times more strongly than either. Calculations show that the binding follows the simple mass law. Similarities between adsorption by microsomes and adsorption by synthetic cation exchange resins are discussed and compared to some of the characteristics of electrolyte behavior in living systems. A possible ion exchange elution, active cation transport mechanism is suggested, involving the preferential elution of Na⁺ out of the cell by H⁺ ions produced by metabolism.

Anesthetic and calcium action in the voltage-clamped squid giant axon

Changes in spike configuration and in the inward and outward currents of voltage-clamped axons agree in indicating that the increases in permeability to sodium and potassium ions during activity are depressed by procaine and cocaine and augmented by calcium. At low levels of depolarization, the effect of the multivalent ion is similar to that of the local anesthetics, in keeping with their similar effects on the threshold of excitability. The reduction of membrane conductance at rest requires a higher concentration of the drugs than that needed to affect the increase in permeability with activity.

Extrarenal action of the adrenal cortex on electrolyte metabolism in nephrectomized and nephrectomized-eviscerated rats

A study was made of the extrarenal action of the adrenal cortex on sodium and potassium metabolism in the rat. There was a reduction in the plasma potassium concentration 24 hours after the administration of desoxycorticosterone, 2 mg/rat, in the adrenalectomized-nephrectomized rat. Treatment with hydrocortisone, 5 mg rat, resulted in the opposite effect. Corticosterone and 2-methyl-9α-fluorohydrocortisone were without effect. In another series of experiments, adrenalectomy resulted in an elevation in the plasma potassium concentration in nephrectomized-eviscerated rats. This change could be detected as early as two hours after operation. The intravenous administration of large doses of desoxycorticosterone, hydrocortisone, corticosterone and aldosterone were without effect. It is suggested that there is a movement of potassium into the extracellular fluid in the absence of the secretions of the adrenal gland.

Ion transport in Nitellopsis obtusa

The distribution and rates of exchange of the ions sodium, potassium, and chloride in single internodal cells of the ecorticate characean, Nitellopsis obtusa, have been studied. In tracer experiments three kinetic compartments were found, the outermost "free space" of the cell, a compartment we have called "protoplasmic non-free space", and the cell sap. The concentrations in the vacuole were 54 mM Na⁺, 113 mM K⁺, and 206 mM Cl^-. The steady state fluxes across the vacuolar membrane were 0.4 pmole Na⁺/cm.² sec., 0.25 pmole K⁺/cm.² sec., and 0.5 pmole Cl^-/cm.² sec. The protoplasmic Na/K ratio is equal to that in the vacuole but protoplasmic chloride is relatively much lower. Osmotic considerations suggest a layer 4 to 6 µ thick with sodium and potassium concentrations close to those in the vacuole. The fluxes between protoplasm and external solution were of the order of 8 pmoles Na⁺/cm.² sec. and 4 pmoles K⁺/cm.² sec. We suggest that the protoplasm is separated from the cell wall by an outer protoplasmic membrane at which an outward sodium transport maintains the high K/Na ratio of the cell interior, and from the vacuole by the tonoplast at which an inward chloride transport maintains the high vacuolar chloride. The tonoplast appears to be the site of the principal diffusion resistance of the cell, but the outer protoplasmic membrane probably of the main part of the potential.

Movements of sodium, potassium and water in rat diaphragm in vitro

Rat diaphragm was incubated for varying periods in Krebs-Ringer media of different osmolarities and in isotonic sucrose media under oxygen at 37°C and 0°C and under nitrogen at 37°C. The importance of metabolic activity on the regulation of water was reestablished for this tissue. In all conditions studied the movements of water were related to the distribution of Na and K. In isotonic media the water content was directly and linearly related to the sum of Na and K in the tissue: for every change of 35.2 mEq Na + K/kg dry weight there was a parallel movement of 1 gm water/100 gm of wet weight. Incubation in the sucrose media caused an immediate and continuous decrease in water under all metabolic conditions. This evidence indicates that the cell is isosmotic to its normal environment and that the regulation of water in diaphragm tissue is direct and passively related to the regulation of the normal tissue electrolytes, or to the distribution and regulation of the solutes present.

The effect of ultraviolet light on the sodium and potassium composition of resting yeast cells

The Na⁺ and K⁺ content of non-metabolizing yeast cells was determined before and after monochromatic ultraviolet (UV) irradiation. UV facilitated the uptake of Na⁺ into and the loss of K⁺ from the cells (net ion flux); the effect is greatest for the shortest wavelength employed (239 mµ) and is partly dependent upon the presence of oxygen. The UV effect on net ion flux persists for at least 90 minutes during which tests were made and it occurs following dosages which are without measurable effect on colony formation. The UV effect on net ion flux is decreased by acidity and promoted by alkalinity. Addition of calcium ions in sufficient amount prevents the usual net ion flux changes observed in irradiated yeast. Increase in concentration gradient between the inside and the outside of the cell increases the net ion flux of irradiated yeast, Na⁺ uptake leading K⁺ loss in all cases. UV appears to act by disorganizing the constituents of the cell surface, permitting K⁺ to leave the cell in exchange for Na⁺. At low intensities of UV this ionic exchange approaches equivalence, but at higher intensities more Na⁺ is taken up than K⁺ is lost. Some evidence suggests that the Na⁺ in excess over that exchanged for K⁺ is adsorbed to charged groups produced by the photochemical effect of UV on the cell surface.

Effect of carbon tetrachloride poisoning on potassium, sodium and water content of liver mitochondria

A physiological test of mitochondrial function, which measures the ability of the mitochondria to concentrate potassium in vitro, was employed in a study of carbon tetrachloride-induced hepatotoxicity. The force feeding of carbon tetrachloride resulted in a) a reduction in the potassium content of rat liver mitochondria, b) an impairment in the ability of potassium depleted mitochondria to reaccumulate potassium and c) an increased water content of the mitochondria. The changes could be demonstrated unequivocally at 10.5 hr. and became extensive at 20 hr. The results do not support the view that the increase in liver fat is the direct result of a lesion in the mitochondria since the time course of impairment in mitochondrial potassium and water metabolism lags behind the fatty changes of the whole liver.

Potassium-dependent sodium extrusion by cells of Porphyra perforata, a red marine alga

Potassium-free artificial sea water causes a loss of cell potassium and a gain of cell sodium in Porphyra perforata, which is not attributable to an inhibition of respiration. On adding KCl or RbCl to such low potassium, high sodium tissues, net accumulation of potassium or rubidium takes place, accompanied by net extrusion of sodium. Rates of potassium or rubidium accumulation and sodium extrusion are proportional to the amount of KCl or RbCl added only at low concentrations. Saturation of rates is evident at KCl or RbCl concentrations above 20–30 mM, suggesting the role of an ion carrier mechanism of transport. Evidence for and against mutually dependent sodium extrusion and potassium or rubidium accumulation is discussed.