PH-DEPENDENCE OF PROTAMINE ACTION ON APICAL MEMBRANE-PERMEABILITY IN NECTURUS GALLBLADDER EPITHELIUM

Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladder tight junctions. Conflicting results, however, have been published whether or not it also affects apical cell membrane permeability. We investigated this issue more systematically by measuring voltage (Ψmc) and fractional resistance (fRa) of the apical membrane at varying concentrations of protamine, K+, and H+ in the bathing solution. At pH 7.6 and [K+] 2.5 mM, (Poler, M.S. and Reuss, L. (1987) Am. J. Physiol. 253, C662) 6 μM protamine caused Ψmc to depolarize from -58 to -51 mV and fRa to decrease from 0.74 to 0.67. If we increased pH to 8.1 these effects were even more pronounded. At [K+] 2.5 mM, but not 4.5 mM, Ψmc transiently hyperpolarized for about 5 min after adding protamine. Most importantly, if [K+] was 4.5 mM and pH was adjusted to 7.1 (Bentzel et al. (1987) J. Membr. Biol. 95, 9) no significant changes of Ψmc and fRa occurred. In any case, at a supramaximal concentration of 200 μM, protamine did not further increase the paracellular response but produced decreasing Ψmc and fRa. We conclude that 6 μM protamine decreases K+ conductance of the apical membrane, if it is already tuned high by high pH. At low control K+ conductance as observed at lower pH, protamine action is restricted to the paracellular pathway. Thus, conflicting results were due to different experimental conditions. At a solution pH of 7.1, 6 μM protamine fulfills criteria of a selective tool for reversibly altering structure and function of the tight junction in Necturus gallbladder. © 1990.