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

Abstract

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 Vsco (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 potential Vo or the inner membrane potential Vi. 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. Vsco 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.

Zinc is a voltage-dependent blocker of native and heterologously expressed epithelial Na+ channels

“…A possible explanation can be found in the work of Adams et al [1], where a single-point mutation in BNaC1 (ASIC2), G430C, created an activatory binding site for Zn 2+ . A similar mechanism could explain the activatory effect of lanthanides applied on the apical side of A6 epithelia (B. Amuzescu, unpublished data) or frog skin [11,12].…”

Voltage dependence of cellular current and conductances in frog skin

“…Employing the sequential technique, Goudeau et al reported a value of V r = 119 mV for skins of Rana esculenta [7]. Using the same technique, Schoen and Erlij found values of 144 and 132 mV in chloride and sulfate Ringer's, respectively, in Rana catesbiana [18].…”

Interpretation of steady-state current-voltage curves: Consequences and implications of current subtraction in transport studies

“…[Amiloride inhibition has been used in this fashion in studies of frog skin (Fuchs et al, 1977;Goudeau et al, 1982) to extract transcellular Na + currents. Likewise, ouabain binding to the animal Na+,K § ATPase, which affects charge movements in both directions (Skou & Norby, 1979;Karlish & Stein, 1982), meets this criterion.]…”

“…Difference I-V characteristics derived in this fashion have been used to characterize both primary electrogenic ion pumps and secondary transport of organic and inorganic solutes in the fungus Neurospora (Gradmann et al, 1978;Sanders et al, 1983;Blatt et al, 1984;, the giant algae Acetabularia (Gradmann, 1975) and Chara (Walker et al, 1979;Beilby & Walker, 1981 ;Beilby, 1984;Kishimoto et al, 1984;Takeuchi et al, 1985), and a liverwort, Riccia (Felle, 1980(Felle, , 1981aJohannes & Felle, 1985). Current subtractions of steady-state I-V curves have also been used to extract voltage-dependent features for active Na + transport in snail neurones (Kostyuk et al, 1972), a putative K + conductance in L-cells (Roy & Okada, 1978), and ionic components of transcellular pathways in frog skin (Fuchs et al, 1977;Goudeau et al, 1982). Now, there are two main assumptions which underly current subtraction.…”

“…This problem has been most acutely felt in studies of plant cells and microorganisms for which, unlike most animal tissues (cf. Marmor, 1971;Kostyuk et al, 1972;Mandel & Curran, 1973;Fuchs et al, 1977;Roy & Okada, 1978;Goudeau et al, 1982; see also Chapman et al, 1979), voltage spans of 200 to 300 mV are generally accessible (Gradmann, 1975;Gradmann et al, 1978;Felle, 1981aFelle, , 1982, and from which a corresponding degree of kinetic information might be gained.…”