MEMBRANE-PROPERTIES OF THE GRANULE CELLS OF THE ISLANDS OF CALLEJA OFTHE RAT STUDIED IN-VITRO

1. Using patch-clamp techniques, we have studied granule neurones from the islands of Calleja in vitro: as isolated cells or as groups of va rying numbers following enzymic digestion, or within untreated slices of similar to 100 mu m thickness. 2. Recordings were made with patch p ipettes in conventional or nystatin-perforated whole-cell mode. Curren t-clamp recordings indicated that these granule cells are excitable an d at resting potential produce irregular spontaneous activity. In volt age clamp the transient inward current underlying these action potenti als could be evoked. This current had a threshold for activation of ab out -50 mV and was sensitive to TTX. In some cells a TTX-resistant tra nsient inward current was observed with a threshold for activation of about -70 mV. 3. Island of Calleja granule cells also exhibited outwar d currents. A rapidly activating transient current was observed that w as resistant to TEA and sensitive to 4-AP, and therefore resembled I-A . The current was half-maximally activated at -6 mV and steady-state i nactivation was half-complete at -65 mV. 4. More sustained outward cur rents were also observed. Although some cells appeared to express a Ca 2+-activated K+ current, the most common finding was a rapidly activat ing, slowly inactivating, voltage-dependent K+ current that was sensit ive to TEA and Ba2+ This current resembled M-current more than delayed rectifier but displayed a number of idiosyncratic kinetic properties. Chief amongst these was the accumulation of an inactivating process w hen the current was repeatedly evoked from potentials near the cells' resting value by voltage steps that by themselves produced no observab le inactivation during the voltage command; this behaviour was similar to the 'C-terminal' inactivation exhibited by lymphocytes and certain expressed K+ channel clones (Kv1.3). 5. These results indicate that t he granule cells of the islands of Calleja are excitable and contain a number of additional regulatory conductances. The implications of the se findings in, and the usefulness of this preparation to, the elucida tion of the function(s) of the islands of Calleja are discussed.