Expression of Caenorhabditis elegans neurotransmitter receptors and ion channels in Xenopus oocytes

Abstract

Injection of Caenorhabditis elegans polyA RNA into Xenopus laevis oocytes led to the expression of neurotransmitter receptors that generated some unique responses, including ionotropic ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors as well as receptors that coupled to G proteins, such as those to octopamine, norepinephrine, and angiotensin, which activated the oocyte's own phosphatidylinositol system and calcium-gated chloride channels. The oocytes also expressed chloride-conducting glutamate receptors, muscarinic acetylcholine receptors, and voltage-operated calcium channels. Unexpectedly, serotonin (5-hydroxytryptamine), dopamine, GABA, and kainate did not generate ionic currents, suggesting that the corresponding receptors were not expressed or were not functional in the oocytes. The use of X. laevis oocytes for expressing worm RNA demonstrates that there are many molecular components whose role remains to be clarified in the nematode. Among them are the nature of the endogenous agonists for the octopamine and angiotensin receptors and the subunits that compose the ionotropic ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and the norepinephrine receptors that couple to the phosphoinositide cascade.nematode ion channels ͉ norepinephrine ͉ octopamine ͉ voltage clamp T he nematode Caenorhabditis elegans has become a very useful model to study the development of the nervous system and the crucial process of interneuronal communication (1). The molecular bases underlying this process are highly conserved among metazoans, and neurotransmitters activate plasma membrane receptors that are phylogenetically related. Accordingly, much can be learned about the process of synaptic transmission everywhere by studying the receptors of C. elegans.The genome of C. elegans was completely sequenced several years ago, and computer analyses of the DNA sequence revealed a number of genes coding for some of the classical vertebrate neurotransmitter receptors: acetylcholine, GABA, and glutamate (2). Acetylcholine is the main excitatory neurotransmitter controlling motor functions in C. elegans, and as many as 50 nicotinic and 3 muscarinic receptor genes have been identified (3, 4). Glutamate and GABA play both excitatory and inhibitory roles in the nematode, and several genes coding for many subunits have been already identified (2,5) In addition, several ion channels involved in the process of synaptic transmission, such as the potassium, calcium, and chloride channels, as well as a plethora of G protein-coupled receptor genes have been studied in C. elegans. Clearly, a complete analysis of the diverse products of these genes will require a functional approach using electrophysiological methods (1).For years, many vertebrate ion channels and receptors have been expressed in frog oocytes, where their electrophysiological and pharmacological properties can be studied by using the two-microelectrode voltage-clamp technique (6, 7). However, relatively little has been done concerning the receptors of worm...

Characterization of a Prawn OA/TA Receptor in Xenopus Oocytes Suggests Functional Selectivity between Octopamine and Tyramine

“…For this reason, we tested the effect of tyramine and octopamine on one of the better characterized components, the transient calcium-dependent chloride current that we refer to as I Cl-T after [53] . This current, which has been referred to as I out [50] , [54] , I Cl-2 [55] or I Cl1-T [53] , can be clearly isolated from I D using a specific pulse protocol ( Fig. 6A ) [53] .…”

Getting to the root of neuronal signalling in plant-parasitic nematodes using RNA interference

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The Biology of the (Pro)Renin Receptor

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