Journal of Neurophysiology, Vol 69, Issue 4 1044-1052, Copyright © 1993 by APS

ARTICLES

Serotonin-operated potassium current in CA1 neurons dissociated from rat hippocampus

H. Uneyama, S. Ueno and N. Akaike
Department of Neurophysiology, Tohoku University School of Medicine, Sendai, Japan.

1. The intracellular mechanisms of serotonin (5-HT) response were investigated in dissociated rat hippocampal pyramidal neurons using the nystatin-perforated patch technique. 2. Under voltage-clamp conditions, 5-HT evoked outward currents (I5-HT) with an increase in membrane conductance at a holding potential of -40 mV. The outward current reversed at the K+ equilibrium potential, which shifted 59.4 mV with a 10-fold change in extracellular K+ concentration. 3. The first application of 5-HT on neurons perfused with Ca(2+)-free external solution induced outward currents of I5-HT but the amplitude was diminished dramatically with successive applications. Pretreatment with the membrane-permeant Ca2+ chelator 1,2-bis-(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl ester (BAPTA-AM) also diminished the I5-HT amplitude. 4. Pretreatment with pertussis toxin (PTX) had no effect on I5-HT. 5. The I5-HT was not cross-desensitized with the caffeine-induced outward current but with outward current mediated by the muscarinic acetylcholine receptor. Pretreatment with Li+ significantly enhanced the I5-HT, indicating that I5-HT is involved in the elevation of intracellular free Ca2+ released from inositol triphosphate (IP3)-sensitive Ca2+ store sites but not from the caffeine-sensitive ones. 6. The calmodulin (CaM) antagonists, trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), inhibited I5-HT in a concentration-dependent manner. 7. The Ca2+/CaM-dependent protein kinase II inhibitor 1-[N,O-Bis (5-isoquinolinesulfonyl)-N-methyl-L-tyrosil]-4-phenylpiperazine depressed the I5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

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