Mechanisms of ion channel activation in olfactory receptor cells of the spiny lobster, Panulirus argus

As in any cell, ion channels underlie the active electrical properties of the lobster olfactory receptor cell. Studying the mechanisms of activation of these ion channels is a step toward understanding how the olfactory receptor cell performs its functions.; Somata isolated from olfactory receptor cells contained three voltage-dependent currents: a sustained Ca{dollar}sp{lcub}++{rcub}{dollar} current, a Ca{dollar}sp{lcub}++{rcub}{dollar}-activated K{dollar}sp{lcub}+{rcub}{dollar} current, and a delayed rectifier K{dollar}sp{lcub}+{rcub}{dollar} current. A TTX-sensitive Na{dollar}sp{lcub}+{rcub}{dollar} current occurred predominantly in the axon. Four ion channels were described: a 35 pS voltage-independent Cl{dollar}sp{lcub}-{rcub}{dollar} channel, a 9.7 pS delayed rectifier K{dollar}sp{lcub}+{rcub}{dollar} channel, a 215 pS Ca{dollar}sp{lcub}++{rcub}{dollar}-activated K{dollar}sp{lcub}+{rcub}{dollar} channel and a nonselective cation channel.; Radioimmunoassays of cAMP in preparations containing the outer dendritic segments of the receptor cells, where odor reception and transduction occur, revealed only a low level of adenylate cyclase activity, and no significant changes were evoked by odorants. Intracellular recordings demonstrated that forskolin or cAMP analogs mixed with a phosphodiesterase inhibitor and applied to the outer dendritic segments did not evoke responses directly or cause the cell's odor response to adapt. These results do not support the hypothesis that cAMP mediates transduction in lobster olfactory receptor cells.; A mixture of L-arginine, L-proline, and L-cysteine evoked hyperpolarizing receptor potentials in both P. argus and the American lobster, Homarus americanus, providing an explanation for noncompetitive mixture suppression in order responses. All cells hyperpolarized by this mixture were also depolarized by other odorants, indicating that multiple transduction mechanisms may exist in the same cell.; Histamine directly gated a chloride channel in receptor cell somata. This channel required external histamine for gating, but not GTP-binding proteins, metabolic energy sources, or Ca{dollar}sp{lcub}++{rcub}{dollar}. The conductance of the channel was 66 pS in P. argus and 44 pS in H. americanus. The pharmacology and dose-dependency of this channel indicate that it mediates the suppression of excitability of the lobster olfactory receptor cell caused by histamine.