Potentiation of salivary fluid secretion in ixodid ticks: a new receptor system for gamma-aminobutyric acid.
gamma-Aminobutyric acid (GABA), having minimal intrinsic activity, potentiates dopamine-induced fluid secretion in salivary glands of female ixodid ticks. Because the effect of GABA was similar to that of spiperone, we tested whether these two drugs act at a common recognition site. Potentiation was not augmented when salivary glands were exposed to supramaximal concentrations of spiperone (1 microM) plus GABA (100 microM). (+/-)-Sulpiride (100 microM), a spiperone antagonist in this system, also blocked GABA-induced potentiation. Picrotoxin (100 microM) and (-)-bicuculline (100 microM), two GABA antagonists, blocked GABA-induced and spiperone-induced potentiation. Inhibition of GABA by picrotoxin and (-)-bicuculline was noncompetitive. Muscimol (an agonist at GABAA receptors) also potentiated dopamine-induced secretion. Baclofen (an agonist at GABAB receptors) did not elicit potentiation. We suggest that GABA may function as a neuromodulator for dopamine-induced fluid secretion in tick salivary glands.
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D009118:Muscimol / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D012463:Saliva / Q000187:drug effects / Q000378:metabolism; D013134:Spiperone / Q000494:pharmacology; D013469:Sulpiride / Q000494:pharmacology; D013987:Ticks / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D001640:Bicuculline; D004298:Dopamine; D009118:Muscimol; D010852:Picrotoxin; D011963:Receptors, GABA-A; D013134:Spiperone; D013469:Sulpiride; D005680:gamma-Aminobutyric Acid