Calcium channel types contributing to excitatory and inhibitory synaptic transmission between individual hypothalamic neurons.
The contribution of L-, N-, P- and Q-type Ca2+ channels to excitatory and inhibitory synaptic transmission and to whole-cell Ba2+ currents through Ca2+ channels (Ba2+ currents) was investigated in rat hypothalamic neurons grown in dissociated cell culture. Excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) were evoked by stimulating individual neurons under whole-cell patch-clamp conditions. The different types of high-voltage-activated (HVA) Ca2+ channels were identified using nifedipine, omega-Conus geographus toxin VIA (omega-CTx GVIA), omega-Agelenopsis aperta toxin IVA (omega-Aga IVA), and omega-Conus magus toxin VIIC (omega-CTx MVIIC). N-, but not P- or Q-type Ca2+ channels contributed to excitatory as well as inhibitory synaptic transmission together with Ca2+ channels resistant to the aforementioned Ca2+ channel blockers (resistant Ca2+ channels). Reduction of postsynaptic current (PSC) amplitudes by N-type Ca2+ channel blockers was significantly stronger for IPSCs than for EPSCs. In most neurons whole-cell Ba2+ currents were carried by L-type Ca2+ channels and by at least two other Ca2+ channel types, one of which is probably of the Q-type and the others are resistant Ca2+ channels. These results indicate a different contribution of the various Ca2+ channel types to excitatory and inhibitory synaptic transmission and to whole-cell currents in these neurons and suggest different functional roles for the distinct Ca2+ channel types.
Zeilhofer
H U
HU
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität Erlangen-Nürnberg, Universitätsstrasse 22, D-91054 Erlangen, Germany.
Müller
T H
TH
Swandulla
D
D
D000818:Animals; D001464:Barium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D004594:Electrophysiology; D007031:Hypothalamus / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D001464:Barium