Protamine reversibly decreases paracellular cation permeability inNecturus gallbladder |
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Authors: | Michael Fromm Carlos E. Palant Carl J. Bentzel Ulrich Hegel |
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Affiliation: | (1) Institut für Klinische Physiologie, Freie Universität Berlin, 1000 Berlin 45, Federal Republic of Germany;(2) State University of New York at Buffalo and VA Medical Center, 14215 Buffalo, New York;(3) Present address: Nephrology Division, Sepulveda VA Medical Center, 41343 Sepulveda, Calif.;(4) Present address: Division of Renal Medicine, East Carolina University School of Medicine, 27834 Greenville, N.C. |
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Abstract: | Summary Protamine, a naturally occurring arginine-rich polycationic protein (pI 9.7 to 12), was tested inNecturus gallbladder using a transepithelial AC-impedance technique. Protamine sulfate or hydrochloride (100 g/ml=20 m), dissolved in the mucosal bath, increased transepithelial resistance by 89% without affecting the resistance of subepithelial layers. At the same time, transepithelial voltage (ms) turned from slightly mucosapositive values to mucosa-negative values of approximately +1 to –5 mV. The effect of protamine on transepithelial resistance was minimal at concentrations below 5 g/ml but a maximum response was achieved between 10 and 20 g/ml. Resistance started to increase within 1 min and was maximal after 10 min. These effects were not inhibited by serosal ouabain (5×10–4m) 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. |
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Keywords: | protamine Necturus gallbladder tight junction impedance analysis transepithelial resistance |
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