Ionic currents of Kenyon cells from the mushroom body of the honeybee

Abstract

The mushroom bodies have been suggested to be essentially involved in learning and memory in insects. In the honeybee Apis mellifera they are composed of about 340,000 intrinsic elements, called Kenyon cells, which can be easily separated from all other neurons of the brain. Here we describe a preparation in which we studied ionic currents in the isolated Kenyon cell somata, using tight-seal whole-cell recording. Several outward and inward currents were identified and investigated by the use of pharmacological agents and in ion substitution experiments: a rapidly inactivating A-type potassium current that is completely blocked with 5 mM 4-aminopyridine; a calcium-activated potassium current that is blocked by 1-100 nM charybdotoxin; a delayed rectifier-type potassium current that is only weakly sensitive to tetraethylammonium but is blocked by 100 microM quinidine; a rapidly activating and inactivating, TTX-sensitive sodium current; a persistent sodium current that is both TTX and cadmium sensitive; and a calcium current that is completely blocked at 50 microM cadmium and is affected by verapamil and nifedipine only at high concentrations (100 microM). The currents described here are very similar to currents found in other insect neurons or muscle cells. This preparation will not only facilitate studies concerning the action of transmitters and neuromodulators that are contained within neurons converging onto the Kenyon cells, but will also allow a study of the role of the adenylyl cyclase pathway, elements of which are expressed in Kenyon cells, and are known to be essential for learning in invertebrates.