Effects of various K+ channel blockers on spontaneous glycine release at rat spinal neurons.
Molecular biology approaches have identified more than 70 different K+ channel genes that assemble to form diverse functional classes of K+ channels. Although functional K+ channels are present within presynaptic nerve endings, direct studies of their precise identity and function have been generally limited to large, specialized presynaptic terminals such as basket cell terminals and Calyx of Held. In the present study, therefore, we investigated the functional K+ channel subtypes on the small glycinergic nerve endings (< 1 microm diameter) projecting to spinal sacral dorsal commissural nucleus (SDCN) neurons. In the presence of TTX, whole-cell patch recording of mIPSCs was made from mechanically dispersed SDCN neurons in which functional nerve endings remain attached. Glycinergic responses were isolated by blocking glutamatergic and GABAergic inputs with CNQX, AP5 and bicuculline. The K+ channel blockers, 4-AP, TEA, delta-dendrotoxin, margatoxin, iberiotoxin, charybdotoxin and apamin, significantly increased 'spontaneous' mIPSC frequency without affecting mIPSC amplitude. The results suggest the existence of the following K+ channel subtypes on glycinergic nerve endings that are involved in regulating 'spontaneous' glycine release (mIPSCs): the Shaker-related K+ channels Kv1.1, Kv1.2, Kv1.3, Kv1.6 and Kv1.7 and the intracellular Ca2+ -sensitive K+ channels BKCa, IKCa and SKCa. Ca2+ channel blockers by themselves, including L-type (nifedipine), P/Q-type (omega-agatoxin IVA, AgTX) and N-type (omega-conotoxin GVIA, CgTX), did not alter the 'spontaneous' mIPSC frequency or amplitude, but inhibited the increase of the mIPSC frequency evoked by 4-AP, indicating the participation of L-, P/Q- and N-type Ca2+ channels regulating 'spontaneous' glycine release from the nerve terminals.
Shoudai
Kiyomitsu
K
Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan.
Nonaka
Kiku
K
Maeda
Megumi
M
Wang
Zhi-Ming
ZM
Jeong
Hyo-Jin
HJ
Higashi
Hideho
H
Murayama
Nobuki
N
Akaike
Norio
N
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D005998:Glycine / Q000378:metabolism*; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000378:metabolism; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D005998:Glycine