Indirect evidence for the presence and physiological role of endogenous extracellular ATP in the semicircular canal.
Previous studies have shown that low concentrations of exogenous ATP, added to the perilymphatic fluid, could modify the bioelectrical activity of the isolated semicircular canal of the frog (Rana pipiens). To test the hypothesis that ATP is endogenously present and active in the perilymphatic fluid, the influence of two ATP-purinoceptor antagonists, Reactive Blue 2 and suramin, and of the enzyme, nucleotide pyrophosphatase, were examined. When applied by perilymphatic bath substitution, the three compounds reduced, in a dose-dependent manner, the firing of the afferent fibers monitored in the absence of mechanically-applied stimulation. The response of the afferent fibers, recorded when the sensory cells were mechanically inhibited, was also reduced. No modification of the response of the excitatory phase of the mechanical stimulus was observed in the presence of the two antagonists. In contrast, the signal was significantly reduced by the enzyme. None of the three compounds exhibited an influence on the transepithelial potential, or its variation in response to mechanical stimulation. The ATP-induced modification of the firing rate of the afferent fibers, monitored in the absence of mechanical stimulation, was reduced in the presence of the three drugs. No influence of Reactive Blue 2 and suramin was observed on the increase of the spontaneous firing induced by carbachol. In contrast, the effect of carbachol was decreased by nucleotide pyrophosphatase. The excitatory influence of glutamate on the spontaneous firing was not modified by Reactive Blue 2, while it was slightly increased by suramin and nucleotide pyrophosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)
Aubert
A
A
Department of Otolaryngology, Head and Neck Surgery, Tulane University, School of Medicine, New Orleans, LA 70112-2699, USA.
Norris
C H
CH
Guth
P S
PS
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects; D018698:Glutamic Acid / Q000494:pharmacology; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D011755:Pyrophosphatases / Q000494:pharmacology; D011894:Rana pipiens; D012665:Semicircular Canals; D013498:Suramin / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology
D014227:Triazines; D018698:Glutamic Acid; C012842:Cibacron Blue F 3GA; D013498:Suramin; D000255:Adenosine Triphosphate; D002217:Carbachol; D005982:Glutathione Transferase; D011755:Pyrophosphatases; C021899:nucleotide pyrophosphatase