Outward Currents in Heart Motor Neurons of the Medicinal Leech. Opdyke, Clifford A., Ronald L. Calabrese. Department of Biology, Emory University, 1510 Clifton Road, Atlanta, GA 30322.
APStracts 2:0226N, 1995.
SUMMARY AND CONCLUSIONS
1. Outward currents were studied in isolation in heart motor neurons in the medicinal leech, using the single-electrode voltage-clamp technique. The currents were divided into four distinct types based upon their time and voltage characteristics and sensitivity to external Ca++ concentration. 2. The four types were: a fast transient current, IKA, a slow transient current, IK1, a non-inactivating current, IK2, all measured in a bathing solution in which Co++. substituted for Ca++, and a calcium sensitive current, IK(Ca), which was revealed in a bathing solution containing normal levels of Ca++. 3. The outward currents in heart motor neurons studied in different ganglia possessed differences of quality. For example, heart motor neurons from ganglia 3 or 4 had significantly less IK2 and IK1 than neurons recorded from more posterior ganglia. Heart motor neurons from ganglion 3 often had little or no IK1. Soma input resistance, electrotonic length and soma capacitance measured in heart motor neurons from both anterior and posterior ganglia exhibited no significant differences. 4. IKA started to activate near -45 mV with one-half- maximal activation at -20 mV and was fully inactivated by 0 mV; IK1 started to activate near -45 mV with one-half-maximal activation at -10 mV and was not fully inactivated by 0 mV; IK2 started to activate near -50 mV; IK(Ca) started to activate near -35 mV. The time constant of removal of inactivation for IKA was 25 ms, measured at -80 mV and for IK1 was 380 ms, measured at -40 mV. 5. TEA allowed to diffuse from the inside of the recording microelectrode effectively blocked IKA, IK1, and IK2. Bath applied TEA (25 mM) acted similarly but was less effective, particularly at blocking IK2. Bath applied 4-AP effectively blocked the transient currents IKA, and IK1. A reversal potential of -65 mV was found for the outward currents corresponding to a mix of IK1, and IK2. 

Received 8 September 1995; accepted in final form 19 July 1995.
APS Manuscript Number J567-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.