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First published online November 2, 2007
Journal of Experimental Biology 210, 3962-3969 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006577

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Histamine operates Cl^–-gated channels in crayfish neurosecretory cells

Jorge Cebada and Ubaldo García^*

Department of Physiology, Biophysics and Neuroscience, Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV-IPN), Av. Instituto Politécnico Nacional 2508, San Pedro Zacatenco, 07360 México City, México

^* Author for correspondence (e-mail: ugarcia{at}fisio.cinvestav.mx)

Accepted 3 September 2007

We describe a histamine-activated Cl^– conductance in the X-organ neurons from crayfish Cherax quadricarinatus, which has comparable properties to the homomultimeric histamine-gated ion channels described in Drosophila. Topical application of histamine inhibited spontaneous neuronal firing in the X-organ sinus gland tract, concomitant with an increase in the membrane conductance. In X-organ neurons in culture and under voltage-clamp conditions, histamine evoked outward currents at –40 mV that reversed at the Cl^– equilibrium potential. Histamine sensitivity in these neurons had a half-maximal response (EC₅₀)=3.3±1 µmol l^–1, with a Hill number of 2.6±0.4. The histamine-evoked current was blocked by tiotidine, cimetidine, ranitidine and 256±11 and 483±11 µmol l^–1, respectively) and d-tubocurarine (IC₅₀=21±2 µmol l^–1), but was insensitive to picrotoxin, bicuculline and strychnine. Neither GABA nor glutamate was capable of desensitizing the histamine response, indicating that histamine activates a particular Cl^– conductance. The presence of immunoreactive neurons to histamine in the medulla terminalis with axonal projections to the neuropile suggests a possible histaminergic modulation of the X-organ sinus gland system.

Key words: Cl^–-gated channel, ionotropic histamine receptors, X-organ sinus gland system, peptidergic neuron