ION-CHANNEL PROPERTIES AND EPISODIC ACTIVITY IN ISOLATED IMMORTALIZEDGONADOTROPIN-RELEASING-HORMONE (GNRH) NEURONS

The mechanism of periodic gonadotropin-releasing hormone (GnRH) secret ion from hypothalamic neurons is difficult to elucidate due to the dif fuse distribution of GnRH neurons and the complex interaction of neuro nal inputs onto them. Recent use of transgenic techniques allowed cons truction of an immortalized GnRH neuronal cell line (GT1), which has n euronal markers and secretes GnRH in a periodic fashion. Using the pat ch-clamp recording technique in the whole-cell and nystatin perforated -patch configuration, the present experiments show that this cell line expressed a tetrodotoxin-sensitive Na channel, two types of Ca channe ls, three types of outward K channels and a K inward rectifier. The la tter current was suppressed in some cells by GnRH or somatostatin. In addition, a gamma-aminobutyric acid (GABA) response, presumably throug h GABA(A) receptors, is recorded. In long-term current-clamp recording s, spontaneous depolarizing activity was found to increase, and then d ecrease, between 20-35 min after removal of the cells from serum- and steroid-containing medium. In some cases, more than one cycle of activ ity was seen. Under voltage clamp, an inward current was recorded at s imilar times, with reversal at about - 15 mV. Thus, two mechanisms of cell interaction, GABA(A) responses and feedback through GnRH response s, and one mechanism of endogenous periodic electrical activity were o bserved in these cells, which could synchronize periodic GnRH release.