Putative glycine receptors in Hydra: a biochemical and behavioural study.
Glycine acts as an inhibitory transmitter in the lower brain stem and spinal cord of vertebrate species, while very few data are yet available to support a similar role in invertebrate nervous systems. Here we report the identification and characterization of glycine receptors in the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa) by biochemical and behavioural studies. Saturation experiments revealed the occurrence of one population of binding sites of nanomolar affinity (KD = 33 nm) and low capacity (Bmax = 79 fmol/mg protein) for [(3)H]strychnine. The addition of glycine or taurine (0.1 microm-1 mm) produced a dose-dependent inhibition of [(3)H]strychnine binding. Beta-alanine (0.1-1 mm) did not significantly affect [(3)H]strychnine binding. The pharmacological properties of these receptors compare with those of vertebrate glycine receptors. Stimulation of Hydra polyps by reduced glutathione resulted in a significant increase in the duration of mouth opening in the presence of glycine, taurine or beta-alanine. The enhancement of the response was related both to amino acid (10-100 microm) and to glutathione concentration (1-10 microm). The effects of glycine or its agonists were suppressed by strychnine (1-10 microm). D-serine, a glycine agonist at the vertebrate NMDA receptor, produced opposite effects to those of glycine. The effects of d-serine were suppressed by 5,7-dichlorokynurenic acid but not by strychnine. In vitro, [(3)H]strychnine binding was not displaced by d-serine. These results indicate a dual action of glycine in Hydra tissues. The hypothesis that NMDA receptors may also be present in this elementary nervous system is proposed.
Pierobon
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P
Consiglio Nazionale Delle Ricerche, Istituto Di Cibernetica E. Caianiello, Comprensorio Olivetti, Building 70, via Campi Flegrei 34, I-80078 Pozzuoli, Naples, Italy. p.pierobon@cib.na.cnr.it
Minei
R
R
Porcu
P
P
Sogliano
C
C
Tino
A
A
Marino
G
G
Biggio
G
G
Concas
A
A
D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology*; D005998:Glycine / Q000378:metabolism*; D006829:Hydra / Q000378:metabolism*; D008297:Male; D009420:Nervous System / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018009:Receptors, Glycine / Q000378:metabolism*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
D018009:Receptors, Glycine; D005998:Glycine