The effect of membrane fixed charges on diffusion potentials and streaming potentials

Abstract

SUMMARY1. Electrical potential differences (p.d.'s) have been measured across an in vitro preparation of rabbit gall-bladder.2. When the gall-bladder separates identical bathing solutions, the p.d. is always zero, regardless of the composition of the bathing solution. Hence the gall-bladder is symmetrical: i.e. the mucosal and serosal cell membranes have the same relative permeability coefficients.3. Osmotic water flow causes streaming potentials of up to 20 mV, of a sign indicating greater permeability to cations than to anions.4. At constant osmolarity, streaming potentials increase slightly with NaCl concentration. Streaming potentials decrease considerably with changes in osmolarity resulting from changes in NaCl concentration.5. Diffusion potentials resulting from electrolyte concentration gradients are fitted well by the constant-field equation with the relative permeability coefficients PNa = 1-00, PC1 = 0*33, PK = 2-3. These permeability coefficients are independent of osmolarity and of salt concentration.6. Relative to 0-25 mm-Ca, 5 mm-Ca reduces streaming potentials by 40 %, NaCl diffusion potentials by 62 %, and potassium diffusion potentials by 43 %.7. The aqueous channels through which water and electrolytes traverse the cell membranes of the gall-bladder contain negative fixed charges, which are blocked by Ca. The physiological significance of the charges may be to reduce chloride permeability and thereby to increase the effectiveness of the gall-bladder in concentrating bile.8. The effect of pH, and analogy with surface charges of other cells, suggest that the charges are organic acids of low pKa.

Effects of External Cations and Respiratory Inhibitors on Electrical Potential of the Xylem Exudate of Excised Corn Roots

“…This could result from a net flow of solution to the xylem vessels; i.e., with solution flow the frictional interaction between solute and solvent forced through cation permselective membranes would tend to make the exudate positive and, thus, at a lover PD than expected for passive diffusion. Potentials of this type are known as streaming potentials and have been reported in animal preparations (6). Unfortunately, no information is available on the magnitude of streaming potentials in plaInt roots.…”

The Ultrastructural Route of Fluid Transport in Rabbit Gall Bladder

“…Gall bladders were everted (following the method of Dietschy (1964) and of Diamond and Harrison (1966)) so that the epithelium faced the outside of the resulting sac. A long cannula was inserted into the everted sac, and both sides of the preparation were bathed in NaC1 or NaC1-HCO3 Ringer's solution at 4°C, so that fluid transport was inhibited.…”

“…Eversion per se does not make the gall bladder more susceptible to damage, as shown by the normal transport rates (Dietschy, 1964) and very stable permeability characteristics (Diamond and Harrison, 1966) of everted preparations. Evidently for purely mechanical reasons the cells are more easily damaged by pressures applied from the connective tissue than from the lumen.…”

Capacitance changes in frog skin caused by theophylline and antidiuretic hormone

“…Water movement across the gall bladder (Diamond, 1962;Diamond & Harrison, 1966) and the intestine (Smyth & Wright, 1966) is associated with streaming potentials due to a drag on cations. Alternatively cations moving through memibranes may drag water molecules along with them, causing electro-osmotic effects as shown by frog skin (House, 1964) and nerve (Stallworthy & Fensom, 1966).…”