Protamine reversibly decreases paracellular cation permeability in Necturus gallbladder.
Protamine, a naturally occurring arginine-rich polycationic protein (pI 9.7 to 12), was tested in Necturus gallbladder using a transepithelial AC-impedance technique. Protamine sulfate or hydrochloride (100 micrograms/ml = 20 microM), dissolved in the mucosal bath, increased transepithelial resistance by 89% without affecting the resistance of subepithelial layers. At the same time, transepithelial voltage (psi ms) turned from slightly mucosa-positive values to mucosa-negative values of approximately +1 to -5 mV. The effect of protamine on transepithelial resistance was minimal at concentrations below 5 micrograms/ml but a maximum response was achieved between 10 and 20 micrograms/ml. Resistance started to increase within 1 min and was maximal after 10 min. These effects were not inhibited by serosal ouabain (5 X 10(-4) M) but could be readily reversed by mucosal heparin. The sequence of protamine effect and heparin reversal could be repeated several times in the same gallbladder. Mucosal heparin, a strong negatively charged mucopolysaccharide, or serosal protamine were without effect. Mucosal protamine reversibly decreased the partial ionic conductance of K and Na by a factor of 3, but did not affect Cl conductance. Net water transport from mucosa to serosa was reversibly increased by 60% by protamine. We conclude that protamine reversibly decreases the conductance of the cation-selective pathway through the tight junction. Although this effect is similar to that reported for 2,4,6-triamino-pyrimidinium (TAP), the mechanism of action may differ. We propose that protamine binds to the apical cell membrane and induces a series of intracellular events which leads to a conformational alteration of the tight junction structure resulting in decreased cationic permeability.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D005704:Gallbladder / Q000166:cytology / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D007365:Intercellular Junctions / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009338:Necturus maculosus; D011188:Potassium / Q000378:metabolism*; D011479:Protamines / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*; D014867:Water / Q000378:metabolism
D002712:Chlorides; D011479:Protamines; D014867:Water; D006493:Heparin; D012964:Sodium; D011188:Potassium