Neuronal synchronization and ionic mechanisms for propagation of excitation in the functional network of immortalized GT1-7 neurons: optical imaging with a voltage-sensitive dye.
Immortalized gonadotropin releasing hormone (GnRH) neurons (GT1 cell line) in culture release GnRH in a pulsatile manner, suggesting that GT1 cells form a functional neuronal network. Optical imaging techniques and a voltage-sensitive fluorescent dye (RH795) were used to study the mechanism of neuronal synchronization and intercellular communication in cultured GT1-7 cells (one of the subclones of the GT1 cell line). The majority (79%) of GT1-7 cells in contact with one another revealed synchronized fluctuations in spontaneous neuronal activity. When a cell in contact with other cells was electrically stimulated, the evoked excitation was propagated to neighbouring cells. The ionic mechanisms involved in the propagation of electrical signals between interconnected GT1-7 cells were investigated using various blockers of Na+, Ca2+ and K+ channels. The propagation of stimulus-evoked excitation was prevented by the voltage-dependent Na+ channel blocker tetrodotoxin. It was also prevented by the voltage-dependent Ca2+ channel blockers, Ni+ (nonselective), nimodipine (L-type) and flunarizine (T-type > L-type), but not apparently affected by omega-agatoxin IVA (P- and Q-type) and omega-conotoxin MVIIA (N-type). The propagation was not influenced by the K+ channel blockers, quinine, tetraethylammonium and Ba2+, but in some cases, it was enhanced by 4-aminopyridine (4-AP) and prevented by apamin. These results suggest that voltage-dependent Na+ channels and L- and T-type Ca2+ channels are involved in the propagation of electrical signals in the GT1-7 neuronal network. Ionic mechanisms, through 4-AP- or apamin-sensitive K+ channels, also seem to be involved in the regulation of signal propagation. These mechanisms may underlie the functioning of the neuronal network formed by immortalized GnRH neurons.
Hiruma
H
H
Department of Physiology, Yokohama City University School of Medicine, Japan.
Uemura
T
T
Kimura
F
F
D000818:Animals; D002121:Calcium Channel Blockers; D015220:Calcium Channels / Q000502:physiology; D002450:Cell Communication; D002461:Cell Line, Transformed; D004558:Electric Stimulation; D004594:Electrophysiology; D005456:Fluorescent Dyes; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000502:physiology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin