CHOLINE CHLORIDE ACTIVATES TIME-DEPENDENT AND TIME-INDEPENDENT K+ CURRENTS IN DOG ATRIAL MYOCYTES

Using the whole cell configuration of the patch-clamp technique, we st udied the effect of isotonic replacement of bath sodium chloride (NaCl ) by choline chloride (ChCl) in dog atrial myocytes. Our results show that ChCl triggered 1) activation of a time-independent background cur rent, characterized by a shift of the holding current in the outward d irection at potentials positive to the K+ equilibrium potential (E(K)) , and 2) activation of a time- and voltage-dependent outward current, following depolarizing voltage steps positive to E(K) Because the chol ine-induced current obtained by depolarizing steps exhibited propertie s similar to the delayed rectifier K+ current (I-K), We named it I-KCh The amplitude of I-KCh was determined by extracellular ChCl concentra tion, and this current was generally undetectable in the absence of Ch Cl. I-KCh was not activated by acetylcholine (0.001-1.0 mM) or carbach ol (10 mu M) and could not be recorded in the absence of ChCl or when external NaCl was replaced by sucrose or tetramethylammonium chloride. I-KCh was inhibited by atropine (0.01-1.0 mu M) but not by the M1 ant agonist pirenzepine (up to 10 mu M). This current was carried mainly b y K+ and was inhibited by CsCl (120 mM, in the pipette) or barium (1 m M, in the bath). We conclude that in dog atrial myocytes, ChCl activat es a background conductance comparable to ACh-dependent K+ current, to gether with a time-dependent K+ current showing properties similar to I-K.