J. Membrane Biol. 66, 123-132 (1982) The Journal of Membrane Biology Microelectrode Studies of the Effect of Lanthanum on the Electrical Potential and Resistance of Outer and Inner Cell Membranes of Isolated Frog Skin H. Goudeau*, J. Wietzerbin*, E. Mintz*, M.P. Gingold*, and W. Nagel** * Service de Biophysique, D6partment de Biologie, CEN Saclay 91191 Gif Sur Yvette Cedex, France and ** Physiologisches Institut der Universit~it Mtinchen, Pettenkoferstrasse 12, D-8000 Mtinchen 2, Germany Summary. Microelectrodes were used to investigate the effect of 0.5 mM mucosal lanthanum (La3+) on the intracellular potential and the resistance of outer and inner isolated frog skin (Rana esculenta) cell membranes. Under short-circuit conditions, the transapical membrane potential Vo ~c (mean value=-65.4 _+3.2mV, inside negative) hyperpolarized to -108.7 _+2.3mV in control skins, after addition of the sodium blocker amiloride. Current-voltage curves for the outer and inner membranes were constructed from the amiloride-inhibitable current versus the outer membrane potential V o or the inner membrane potential l/~. The outer, and to a lesser degree the inner, membrane showed a characteristic nonlinearity with two slope resistances. Addition of La 3+ to the outer medium increased the short-circuit current to t90% of the control value. V sc concomitantly changed to -28 +3.5 mV and outer and inner membrane resistances fell, consid- erably attenuating the nonlinearity seen in control skins. La 3+ is suggested to raise the conductance by its effect on the surface potential. A secondary long-term inhibitory effect of La 3+ on short-circuit current has been observed. It is ascribed to the penetration of La 3+ into the sodium channels. Key words frog skin 9 microelectrodes 9 IV curves . lanthanum Introduction According to the well-known model of Koefoed- Johnsen and Ussing (1958) for transepithelial active sodium transport, Na + traverses the epithelial cells by passive entry through the outer membrane and is then actively extruded through the inner or serosal membrane by a (Na § +K+)-ATPase. This active so- dium transport can be electrically described by a transepithelial driving force EN, in series with a re- sistance RN, representing the Na + active transport pathway (Ussing & Zerahn, 1951). When lanthanum (La 3+) is added to the outer side of the isolated frog skin, its initial effect is to increase the active epi- thelial Na § transport, measured as short-circuit cur- rent (Martinez-Palomo, Erlij & Bracho, 1971; De Sousa, 1975; Wietzerbin, Goudeau & Gary-Bobo, 1977; Grinstein, Candia & Erlij, 1978; Goudeau, Wietzerbin & Gary-Bobo, 1979). This transport stimulation is thought to arise from enhanced per- meability of the outer membrane as a result of a surface effect of the trivalent ion which modifies the transapical membrane potential (Grinstein etal., 1978) and possibly intrinsic membrane conductance (Goudeau et al., 1979). However, at present, only a rise in the overall conductance of the active pathway gNa = has been evidenced, without any signifi, cant change in EN, (Goudeau et al., 1979). On the other hand, La 3+ stimulation of Na § transport is transient, since La 3+ presumably has a secondary longterm inhibitory effect on the Na + permeability of the outer membrane. The present study uses a recently developed mi- croelectrode technique to measure intracellular po- tentials in frog skin epithelium (Nagel, 1976, 1977, 1978, 1980; Helman & Fischer, 1977). On control and La3+-treated skins, we measured the outer membrane potential V o at different transepithelial potentials (VcL), with and without the specific so- dium transport blocker amiloride. We established a nonlinear relationship between amiloride-inhibitable current (i.e. Na§ current), and the transmem- brane potentials. We observed that La 3 § : 1) changes the outer cell membrane electrical gradient existing under short-circuit conditions; 2) increases outer membrane conductance and to a lesser degree inner membrane conductance; 3) flattens the rectification exhibited by both membranes, and 4) has a long-term effect mainly manifested by a secondary decrease in outer membrane conduc- tance. 0022-2631/82/0066-0123 $02.00 9 1982 Springer-Verlag New York Inc.