Swimming behavior regulation by GABAB receptors in Paramecium.
In Paramecium, internal Ca(2+) concentration increase coupled to membrane depolarization induces a reversal in the direction of ciliary beating and, consequently, a reversal in swimming direction. The ciliary reversal (CR) duration is correlated to Ca(2+) influx, and the addition of drugs that block the Ca(2+) current leads to a reduction in the backward swimming duration. In this study we have examined the possible function of GABA(B) receptors in P. primaurelia swimming control. The presence of GABA(B) immunoanalogue in Paramecium was evidenced using SDS-PAGE, Western blotting, and confocal laser scanning microscopy. By applying the specific GABA(B) receptor agonist baclofen, a dose-dependent inhibition of the membrane depolarization-induced CR duration was observed. This inhibition was antagonized by phaclofen, persisted when K(+) channel blockers were applied, and disappeared after treatment with nifedipine and verapamil. Moreover, the action of baclofen on depolarization-induced CR was suppressed by treatment with pertussis toxin. Therefore, these experiments suggest that baclofen modulates CR by a G protein (G(0) or G(1)) mediated inhibition of dihydropyridine-sensible calcium channels. Finally, synthesis and release of GABA in the environment by Paramecium have been demonstrated by HPLC. Possible correlations between GABA(B) receptor activation and the regulation of intracellular Ca(2+) levels are discussed.
Ramoino
Paola
P
Department for the Study of Territory and its Resources (DIP.TE.RIS.), University of Genoa, Corso Europa 26, 16132 Genova, Italy. ramoino@dipteris.unige.it
Fronte
Paola
P
Beltrame
Francesco
F
Diaspro
Alberto
A
Fato
Marco
M
Raiteri
Luca
L
Stigliani
Sara
S
Usai
Cesare
C
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002923:Cilia / Q000378:metabolism* / Q000502:physiology; D058786:GABA-B Receptor Agonists; D019204:GTP-Binding Proteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009043:Motor Activity; D010247:Paramecium / Q000502:physiology*; D018080:Receptors, GABA-B / Q000302:isolation & purification / Q000502:physiology*; D013550:Swimming / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis
D015220:Calcium Channels; D058786:GABA-B Receptor Agonists; D018080:Receptors, GABA-B; D005680:gamma-Aminobutyric Acid; D019204:GTP-Binding Proteins; D001418:Baclofen; D002118:Calcium