Effects of lanthanides on voltage-dependent potassium currents in bullfrog sympathetic neurons

Abstract

The effects of lanthanides (La 3+, Gd 3+, Lu 3+ and Sm 3+) on voltage-dependent potassium currents were studied in dissociated bullfrog sympathetic neurons. A-type current ( I A) and M-type current ( I M) were blocked by lanthanides (0.1–30 μM) with I M being much less sensitive to these ions than I A. The order of potency was Gd 3+≥Lu 3+≈La 3+≈Sm 3+ for I A and Gd 3+≫Lu 3+≈La 3+>Sm 3+ for I M. The I M block occurred independently of its activation kinetics while the I A block was associated with a positive shift of the activation and inactivation curves. Gd 3+ (100 μM) blocked the delayed rectifier-type current ( I K) by less than 20%; Lu 3+, La 3+ and Sm 3+ (100 μM for each) were without effect on I K. It is concluded that I A was the most sensitive to lanthanides, and Gd 3+ was the most potent for all the currents in amphibian autonomic neurons.