Histamine decreases calcium-mediated potassium current in guinea pig hippocampal CA1 pyramidal cells.
The action of histamine on CA1 pyramidal cells was studied in a hippocampal slice preparation. In the presence of tetrodotoxin (TTX) and tetraethylammonium (TEA), histamine had little effect on the calcium spikes. Using the single-electrode voltage-clamp technique, the actions of histamine on membrane currents were tested. In TTX, histamine (1 microM) decreased outward current only at potentials more depolarized than approximately -50 mV, where calcium-mediated potassium current is predominant. In the presence of manganese, histamine was without effect. Histamine (10 microM) did not affect the transient outward potassium current (A-current), the inward M-current resulting from small hyperpolarizing steps, or the inward Q-current elicited by larger hyperpolarizing steps. Blocking potassium currents with TEA or replacing calcium with barium revealed a slow inward current normally carried by calcium. With TTX present to block sodium currents, histamine (10 microM) did not reduce the inward current. The outward current reduced by a maximally effective concentration of histamine (10 microM) can be further decreased by manganese. The results support the conclusion that histamine selectively decreases the calcium-mediated potassium conductance in CA1 pyramidal cells of hippocampus. The possibility is raised that there is a component of calcium-mediated potassium current that is insensitive to histamine.
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D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004553:Electric Conductivity; D006168:Guinea Pigs; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D006632:Histamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D013757:Tetraethylammonium Compounds; D008345:Manganese; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D009116:Muscarine; D006632:Histamine; D011188:Potassium; D002118:Calcium