A study of the mechanism of water transfer across frog skin by a comparison of the permeability of the skin to deuterated and tritiated water

Pulse nuclear magnetic resonance measurements of water exchange across the erythrocyte membrane employing a low Mn concentration

A simple, precise, and rapid pulse nuclear magnetic resonance technique for measuring the rate of water exchange across the erythrocyte membrane is presented. The technique is based upon the nonlinear fit of Carr-Purcell-Meiboom-Gill (CPMG) transverse relaxation time data of blood doped with 1.7 mM MnCl2 to the general two-compartment exchange condition. Previous approaches using CPMG data required high MnCl2 concentrations (25-53 nM), shown in this work to induce systematic errors ranging from 35 to 45%. At 23 degrees C the average residence time of a water molecule inside the erythrocyte (tau a) is 21.0 +/- 0.6 ms (SE). The Arrhenius plot for water exchange is linear over the range of 3 degrees - 37 degrees C and th Arrhenius activation energy is 4.79 +/- 0.03 kcal (SE). This value does not differ significantly from the energy required for bulk water flow. Results are compared with previous determinations, and sources of systematic error in tau a and the activation energy are evaluated.

[Influence of environmental salinity on the diffusion fluxes of water in the Isopod Sphaeroma serratum (Frabricius)]

1.--In Sphaeroma serratum, the diffusion fluxes of water are 3 or 4 times more important in sea water (SW) than in diluted (50%) sea water. In 100% and in 50% SW influx equals the outflux. 2.--When the animal is quickly transferred from 100% SW to 50% SW, and from 50% SW to 100% SW, the outflux is instantaneously and entirely reset. 3.--The main factor of the instantaneous resettlement of the outflux seems to be the variation of the concentration of Na+ or Cl- or both together in the external medium; the Ca2+ and Mg2+ concentrations do not seem to have any effect on the diffusion flux. 4.--The validity of our results is discussed (theory of unstirred layers, blood-circulation, oxygen interchange, ultrastructure). Our results are compared with those obtained in other Crustaceans and in Fishes.

Transport of deutherium oxide across isolated rat small intestine

1. Transport of deuterium oxide from a luminal perfusate containing 1% D2O was studied in Fisher & Gardners (1974) isolated preparation of perfused rat small intestine. 2. The kinetics of appearance of D2O in the intestinal secretion at the serosal surface fitted well to a single exponential function. 3. The steady-state concentration of D2O in this secretion was not significantly different from the concentration in the luminal perfusate. 4. The total tissue water contained D2O at a concentration, on average, 5% lower than that in the luminal perfusate. 5. There is no evidence to suggest discrimination in transport across the intestinal mucosa between H2O and D2O. 6. The kinetics of wash-in of D2O to intestinal secretion show that the ratio of flux out of the lumen to reflux back to the lumen is 1-38;1.

Structure and function in urinary bladder of foetal sheep

1. The structure and function of the epithelial lining of the urinary bladder of sheep foetuses was investigated by electron microscopic studies made in conjunction with a series of experiments in which the permeability of the bladder to sodium and water was measured in vitro. Measurements were made at gestational ages ranging from 50 to 141 days (term = 147 days) Osmolarity and electrolyte concentrations of urine found in the foetal bladder were also measured.2. The development of tight junctions between the bladder epithelial cells was investigated by incubating the tissue with solutions containing 1 mM-LaCl(3) on the mucosal surface. No penetration of the junctions by lanthanum was observed in foetuses of 90 days or older. In younger bladders, the epithelial layer was stripped by treatment with lanthanum, but tight junctions appeared to be fully developed in early bladders incubated without lanthanum.3. The surface structure of the luminal (mucosal) plasmalemma was fully developed at 50 days.4. Unidirectional fluxes of labelled sodium and water were measured with identical solutions bathing the two surfaces of the bladder wall. No net water movement occurred; the mean ratio of efflux to influx in nine bladders was 1.002 +/- 0.039 (S.E. of mean). Under these conditions, the flux ratio for sodium was 1.735 +/- 0.143 (S.E. of mean) in twelve bladders.5. Antidiuretic hormone (ADH) had no effect on net water movement but reduced the net efflux of sodium so that the flux ratio became 1.285 +/- 0.255 (S.E. of mean) n = 8. ADH also had a striking effect on the structure of the epithelium, causing marked swelling of the intercellular spaces. The tight junctions remained an effective barrier to lanthanum penetration under these conditions; lanthanum was not observed in the enlarged spaces.

Permeation and distribution of deuterated and tritiated water in smooth and striated muscle

1. The diffusion of deuterated water (HDO) into and out of isolated guinea-pig taenia coli and frog sartorius was followed by means of a recording electronic microbalance.2. A comparison was made of the rates of efflux of deuterated and tritiated (HTO) water using the microbalance and a standard tracer technique.3. The time course of the exchange of HDO in both smooth and striated muscle was fitted to the sum of two exponential functions; however, it was not possible to correlate sizes of the intra- and extracellular spaces in the muscles with the sizes of the two compartments in model systems based on compartmental theory of tracer kinetics.4. The efflux of HDO, which was measured by means of the microbalance under stagnant conditions, occurred at a rate approximately 3 times slower than the efflux of HTO which took place while muscles were agitated vigorously in their bathing media.5. There was a marked deviation at short times from a double exponential time course during the efflux of HTO.6. Values of the tracer water permeability, P(d), of smooth and striated muscle fibres, and the extracellular space, E, of the muscles were obtained using a computer to numerically evaluate the series solutions of the equations describing the permeation of labelled water in the muscles.7. It was necessary to assume a value for the diffusion coefficient of the tracer in extracellular fluid in order to compute a unique fit to an exchange curve.8. Values of P(d) and E given by the analysis depended upon the method used for monitoring the exchange, and an interpretation of this dependence was made difficult by the variation in the thickness of unstirred layers on the surface of the muscles under the different experimental conditions.