Effects of quinine on three different types of potassium currents in bullfrog sympathetic neurons

Whole-cell/voltage-clamp recordings were made from dissociated bullfrog sym pathetic neurons to examine the sensitivity of potassium currents to a pota ssium channel blocker quinine (1-500 mu M). Among th ree currents tested, a rapidly inactivating A-type current (I-A) was the most sensitive to the bl ock by quinine (IC50 approximate to 22 mu M). A non-inactivating M-type cur rent (I-A) was the least sensitive (IC50 approximate to 445 mu M), and the sensitivity of a slowly inactivating delayed rectifier-type current (I-K) w as in between (IC50 approximate to 115 mu M). Results suggest that the abil ity of quinine to block different types of potassium currents such as I-A a nd I-M with significantly different IC50 values would be of help for the po tassium channel pharmacology in amphibian autonomic ganglion cells. (C) 199 9 Elsevier Science Ireland Ltd. All rights reserved.