Ionic conductances in two types of sensory neurons in the leech, Macrobdella decora

1. Ion conductances were investigated in two kinds of leech sensory neurons (PM and N1 cells) which differ in their membrane excitability and action potential. 2. In the PM cell body excitable membrane behavior is dominated by only two currents, a sodium current (INa) and a delayed rectifier (IK). 3. In contrast, in the N1 cell INa and IK is supplemented with the presence of a transient potassium current, IA. 4. A comparison between INa and IK in the two cell types did not reveal any significant difference in activation and inactivation kinetics of either current between neurons. 5. Thus, the properties and presence of the A-current in the N1 cell and not in the PM cell may account for the functional difference in excitability of the two kinds of neurons.