Journal of Neurophysiology, Vol 74, Issue 6 2524-2537, Copyright © 1995 by APS

ARTICLES

Outward currents in heart motor neurons of the medicinal leech

C. A. Opdyke and R. L. Calabrese
Department of Biology, Emory University, Atlanta, Georgia 30322, USA.

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 on the basis of their time and voltage characteristics and sensitivity to external Ca2+ concentration. 2. The four types were a fast transient current, IKA; a slow transient current. IK1; a noninactivating current, IK2, all measured in a bathing solution in which Co2+ was substituted for Ca2+; and a calcium-sensitive current. IK1Cal which was revealed in a bathing solution containing normal levels of Ca2+. 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 half-maximal activation at about -20 mV and was fully inactivated by 0 mV: IK1 started to activate near -45 mV with half-maximal activation at about -10 mV and was not fully inactivated by 0 mV; IK2 started to activate near -50 mV; IK1Cal started to activate near -35 mV. The time constant of removal of inactivation for IKA was 25 ms, measured at -80 mV, and that for IK1 was 380 ms, measured at -40 mV. 5. Tetraethylammonium acetate (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-aminopyridine 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.

This article has been cited by other articles:

				P. S. Garcia, T. M. Wright, I. R. Cunningham, and R. L. Calabrese Using a Model to Assess the Role of the Spatiotemporal Pattern of Inhibitory Input and Intrasegmental Electrical Coupling in the Intersegmental and Side-to-Side Coordination of Motor Neurons by the Leech Heartbeat Central Pattern Generator J Neurophysiol, September 1, 2008; 100(3): 1354 - 1371. [Abstract] [Full Text] [PDF]

				B. J. Norris, A. L. Weaver, A. Wenning, P. S. Garcia, and R. L. Calabrese A Central Pattern Generator Producing Alternative Outputs: Pattern, Strength, and Dynamics of Premotor Synaptic Input to Leech Heart Motor Neurons J Neurophysiol, November 1, 2007; 98(5): 2992 - 3005. [Abstract] [Full Text] [PDF]

				B. J. Norris, A. L. Weaver, L. G. Morris, A. Wenning, P. A. Garcia, and R. L. Calabrese A Central Pattern Generator Producing Alternative Outputs: Temporal Pattern of Premotor Activity J Neurophysiol, July 1, 2006; 96(1): 309 - 326. [Abstract] [Full Text] [PDF]