ADENOSINE MODULATION OF POTASSIUM CURRENTS IN PREGANGLIONIC NERVE-TERMINALS OF AVIAN CILIARY GANGLIA

Potassium currents in calyciform nerve terminals of the avian ciliary ganglion were analyzed using a single microelectrode voltage clamp. The modulatory affects of adenosine on these currents was also determined. Intracellular CsCl (1 M) blocked the steady-state outward current, indicating that it is mostly carried by K+. Tetraethylammonium (TEA, 10 mM) blocked over 40% of the outward current at a command potential of -30 mV. If Ca2+ influx was blocked by CoCl2 (5 mM), the steady-state outward current was reduced by over 16% in the nerve terminals suggesting that about one fifth of the outward current passes through calcium-activated potassium channels I(K)(Ca). Adenosine (50 mM) decreased the outward steady-state current over a wide range of command potentials in most terminals studied but failed to decrease this current in the presence of CoCl2 (5 mM). It is concluded that adenosine blocks I(K)(Ca) in nerve terminals.