Microelectrode studies of the effect of lanthanum on the electrical potential and resistance of outer and inner cell membranes of isolated frog skin

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Abstract
Microelectrodes were used to investigate the effect of 0.5mm 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 potentialV o sc (mean value=−65.4±3.2 mV, inside negative) hyperpolarized to −108.7±2.3 mV 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 potentialV o or the inner membrane potentialV t . The outer, and to a lesser degree the inner, membrane showed a characteristic nonlinearity with two slope resistances. Addition of La3+ to the outer medium increased the short-circuit current to 190% of the control value.V o sc concomitantly changed to −28±3.5 mV and outer and inner membrane resistances fell, considerably attenuating the nonlinearity seen in control skins. La3+ is suggested to raise the conductance by its effect on the surface potential. A secondary long-term inhibitory effect of La3+ on short-circuit current has been observed. It is ascribed to the penetration of La3+ into the sodium channels.