EFFECTS OF BARIUM, LANTHANUM AND GADOLINIUM ON ENDOGENOUS CHLORIDE AND POTASSIUM CURRENTS IN XENOPUS OOCYTES

1. The effects of multivalent cations on membrane currents recorded fr om Xenopus oocytes were studied. 2. The hyperpolarization-activated ch loride current was reversibly blocked by lanthanum; half-maximal block occurred at a concentration of 8 mu M. Zinc, cadmium, cobalt and nick el were less potent than lanthanum, and gadolinium, manganese, barium and strontium had no effect at a concentration of 100 mu M. 3. The cal cium-activated chloride current was blocked by gadolinium (50 mu M), a nd lanthanum, cadmium, cobalt, nickel and manganese were equally effec tive. The actions of gadolinium and lanthanum were almost irreversible , while partial (30-80%) recovery was observed with tile other cations . Zinc (100 mu M) had no effect. 4. In lanthanum (100 mu M), membrane depolarizations from -70 mV activated an outward potassium current tha t was partially blocked by barium (0.1-2 mM). The barium-sensitive cur rent was confined to potentials less negative than -70 mV. The current consisted of a time-independent as well as a time-dependent component , the latter of which had voltage dependence similar to the M-current. 5. It is proposed that lanthanum, gadolinium and barium can usefully separate these endogenous membrane currents in Xenopus oocytes.