Cyclic nucleotide- and inositol phosphate-gated ion channels in lobster olfactory receptor neurons.

Abstract

The idea of having two second pathways In ofa , one mediated by cAMP aNd the other by bnosytol 1,4,5-trispbosphate, Is tation and inhibition of lobster ORNs are mediated by InsP3 and cAMP transduction cascades would be to demonstrate the presence of InsP3-and cAMP-activated ion channels at the presumed site of transduction, the outer dendritic membrane, in lobster ORNs in situ.Here, we report that cAMP and InsP3 applied to the inner face of cell-free patches of the outer dendritic membrane of lobster ORNs in situ directly activate distinct ion channels, that both types of second messenger-gated channels can occur in the same patch, and that the InsP3-gated channels, and possibly the cAMP-gated channels, can be one of two types. A preliminary description of these results has appeared (24).Odors are generally thought to activate olfactory receptor neurons (ORNs) through guanine nucleotide binding proteincoupled receptors that elicit rapid and transient pulses of intracellular second messengers (for reviews, see refs. 1-3). Attention has focused on two second messenger pathways, one mediated by cAMP and the other by inositol 1,4,5-trisphosphate (InsP3). cAMP and InsP3 olfactory transduction cascades have been identified in four groups of animals (mammals, refs. 4-6; amphibians, refs. 7 and 8; fish, refs. 9 and 10; crustaceans, refs. 11 (25), so the excised tips should contain only outer dendritic membrane and microtubules. Care was taken to include <50% of the length of the sensillum in the excised tips. Outer dendrites were placed in poly(D-lysine)-coated plastic dishes containing 5 ml of isolation buffer (460 mM

Molecular Cloning of a Lobster Gαq Protein Expressed in Neurons of Olfactory Organ and Brain

“…This suggests that both pathways can coexist in a single ORN. In lobster ORNs this coexistence was established in single-cell recordings of the summation of depolarizing receptor potentials caused by odor-evoked InsPproduction and hyperpolarizing receptor potentials caused by odorevoked cAMP production (McClintock and Ache, 1989b;Michel et al, 1991;Fadool and Ache, 1992;Boekhoff et al, 1994;Hatt and Ache, 1994;Michel and Ache, 1994). The discovery that virtually all odorants can cause depolarizations in one lobster ORN but hyperpolarizations in another supports the hypothesis that this interaction is a mechanism of coincidence detection that allows a smaller number of ORNs to efficiently encode sophisticated information.…”

“…both. Previous studies have implicated the InsP3 pathway and Ga,4 in excitatory olfactory transduction in lobsters, especially in P. argus (Fadool and Ache, 1992;Boekhoff et al, 1994;Hatt and Ache, 1994;Fadool et al, 1995). Substantial evidence exists to suggest that two lobsters (Bayer et al, 1989;McClintock and Ache, 1989a,b).…”

“…Odor responses are dependent on G proteins, odorants stimulate inositol phosphate production in outer dendritic membranes, inositol phosphates can activate several cation channels in the somatic and outer dendritic plasma membrane, and blockers of these channels also block odor responses Ache, 1992, 1994;Boekhoff et al, 1994;Hatt and Ache, 1994). The lack of sensitivity of odor responses to pertussis toxin preResubmitted manuscript…”

Evidence for the Involvement of Inositol Trisphosphate but Not Cyclic Nucleotides in Visual Transduction in HermissendaEye

“…Although the primary role of IP 3 has been considered to be the release of Ca 2ϩ from intracellular stores, several IP 3 -gated ion channels have been recently characterized in olfactory cilia (37,38) and rat megakaryocytes (39), raising the possibility that IP 3 directly activates a transduction channel in Hermissenda.…”

“…The present study focuses on investigating the second messengers underlying the initial Na ϩ current component of the photoresponse. Recently, channels directly gated by IP 3 have been described in other cell lines (37,38), including Na ϩ channels in rat megakaryocytes (39). This raises the possibility that the native photoresponse in Hermissenda is generated by an IP 3 -gated Na ϩ channel.…”