Effects of lanthanides on voltage-dependent potassium currents in bullfrogsympathetic neurons

The effects of lanthanides (La3+, Gd3+, Lu3+ and Sm3+) on voltage-dependent potassium currents were studied in dissociated bullfrog sympathetic neuron s. A-type current (l(A)) and M-type current (l(M)) were blocked by lanthani des (0.1-30 mu M) with l(M) being. much less sensitive to these ions than I A The order of potency was Gd3+ approximate to Lu3+, La3+ approximate to Sm 3+ for IA and Gd3+ much greater than Lu3+, La3+ > Sm3+ for l(M). The l(M) b lock occurred independently of its activation kinetics while the IA block w as associated with a positive shift of the activation a nd inactivation cur ves. Gd3+ (100 mu M) blocked the delayed rectifier-type current (l(K)) by l ess than 20%; Lu3+, La3+ and Sm3+ (100 mu M for each) were without effect o n l(K). It is concluded that l(A) was the most sensitive to lanthanides, an d Gd3+ was the most potent for all the currents in amphibian autonomic neur ons. (C) 2000 Published by Elsevier Science Ireland Ltd.