CHARACTERIZATION OF THE K-HT1A RECEPTOR IN THE ACUTELY DISSOCIATED RAT DORSAL RAPHE NEURONS( CURRENT MEDIATED BY 5)

The action of 5-hydroxytryptamine (5-HT) via the 5-HT1A receptor on di ssociated rat dorsal raphe neurons was characterized under the whole-c ell mode by using the nystatin-perforated patch-clamp technique. Under voltage-clamp conditions, 5-HT induced an inwardly rectifying K+ curr ent (I5-HT) in a concentration-dependent manner. I5-HT was mimicked by 8-OH-DPAT and buspirone, which are both 5-HT1A receptor agonists. I5- HT was reversibly blocked by such 5-HT1A receptor antagonists as (S)-U H-301 and spiperone but not by ketanserin, a 5-HT2 receptor antagonist , granisetron, a 5-HT3 receptor antagonist, and GR-113808, a 5-HT4 rec eptor antagonist. I5-HT was antagonized concentration-dependently by s uch K+ channel blockers as quinine, Ba2+ and 4-aminopyridine but was r elatively insensitive to both Cs+ and tetraethylammonium. When the neu rons were loaded with guanosine 5'-O-3-thiotriphosphate through a patc h pipette, the K+ current induced by 5-HT became irreversible. N-ethyl maleimide (NEM), a sulfhydryl alkylating agent, irreversibly blocked I 5-HT. The intracellular perfusion with ,2-bis(2-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid (BAPTA), a Ca2+ chelator, or neomycine, a pho spholipase C inhibitor, never significantly affected the 5-HT-induced response. 12-Myristate 13-acetate diester (PMA), a protein kinase C (P KC) activator, had only a weak inhibitory effect on I5-HT, and stauros porine, a PKC inhibitor, failed to significantly occlude I5-HT. Theref ore, the K+ conductance activated via the 5-HT1A receptor of dorsal ra phe neurons was thus characterized by the sensitivity to such K+ chann el blockers as quinine, Ba2+ and 4-aminopyridine. Moreover, G protein, which is NEM-sensitive and can couple to the 5-HT1A receptor, is thus considered to activate the inwardly rectifying K+ conductance without being mediated by such second messengers as Ca2+ and PKC.