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Chloride movement across the wall of the rabbit submaxillary duct has been studied. It was shown that the chloride diffusion from blood to luminal side was determined primarily by the existing transmucosal potential difference. From the fact that the ouabainpoisoned duct showed symmetrical behavior with respect to the chloride diffusion potentials in both directions and the fact that the measured chloride flux behaved as predicted according to the Goldman equation, it was suggested that a single barrier, rather than a series membrane system, determined the chloride movement. The permeability coefficients for chloride, in the order of 5.5×10 cm sec are much larger than would be expected for cell membranes. These findings in combination with the observation that mannitol permeability is higher during chloride perfusion than during sulfate perfusion and the observed electron-microscopic changes favor the concept of the existence of an extracellular route in chloride diffusion. An equivalent electrical circuit is given in order to evaluate the contribution of the chloride shunt more quantitatively. Calculations showed that the ductal resistivity during sulfate perfusion has a value in the order of 434 Ω cm, while during chloride perfusion this value is lowered to 48 Ω cm, indicating that the ductal wall can change from a tight to a leaky epithelium. The implications of these findings are discussed. [ABSTRACT FROM AUTHOR]

The permeability of the glomerular capillary wall to neutral macromolecules was studied in isolated perfused rat kidneys. Pluronic F108 (BASF, Wyandotte, MI, USA), a polyoxyethylene-polyoxypropylene block copolymer of mol weight ∼14,000, was used as plasma expander. Pore theory was applied to the fractional clearances of Pluronic F108 and dextran (mol weight 19,400) molecules measured both as a function of glomerular filtration rate. Using the pore model of Verniory et al. [30] the effective pore radius (60.9 Å) and the ratio of total pore area and pore length (4.0 cm/nephron) were estimated, and a hydraulic permeability coefficient K (0.036 nl/s·mm Hg) was calculated. There was no significant difference between the fractional clearance of Pluronic F108 obtained with different Pluronic F108 concentrations over the range 15-35 g/l, hence with largely differing osmotic pressures. It was concluded that the sieving properties of the glomerular membrane of the isolated perfused rat kidney are not detectably different from those in the intact rat, at least in the case of uncharged macromolecules. [ABSTRACT FROM AUTHOR]

Glomerular hemodynamics were studied of isolated perfused kidneys of 12-wk-old normotensive (NR) and spontaneously hypertensive (SHR) rats, using Pluronic F108 (BASF, Wyandotte, MI, USA) as a plasma expander. Glomerular filtration rate (GFR), proximal tubular hydrostatic pressure ( P) and glomerular capillary hydrostatic pressure ( P) were approximately linearly related with renal perfusion pressure. P measured directly by micropuncture was comparable to P calculated from other parameters of glomerular dynamics using pore theory. We conclude that GFR in isolated kidneys perfused with Pluronic F108 is lower than in vivo, mainly as a result of an increase in P. This rise in tubular pressure is due to an increased urine flow rate and an elevated tubular fluid viscosity. The difference in glomerular dynamics between NR and SHR kidneys is the result of an increased preglomerular vascular resistance in SHR, possibly due to an adaptive hypertrophic reaction to a sustained hypertension. [ABSTRACT FROM AUTHOR]

The hypertonicity of the secretory fluid produced by the cat sweat gland is due to a potassium release mechanism which operates in series with an isosmotic NaCl transport process. The potassium excretion rate is not coupled with volume flow but is determined by the frequency of electrical stimulation. Evidence is presented for the presence of two potassium release mechanisms during the secretory process. A small potassium flux is due to cellular redistribution at the onset of stimulation potassium secretion perhaps originating from dark cells. The major potassium flux is related to the bicarbonate excertion rate. [ABSTRACT FROM AUTHOR]