P2 purinoceptor of the globular substance in the otoconial membrane of the guinea pig inner ear.
The biological characteristics of the globular substance, a precursor of otoconia, are unclear. In the present study, the ATP-induced internal free Ca2+ concentration ([Ca2+]i) changes of the globular substance and the ATP distribution in the vestibular organ were investigated using a Ca2+ indicator, fluo 3, and an adenine nucleotide-specific fluorochrome, quinacrine, by means of confocal laser scanning microscopy. [Ca2+]i showed a rapid and dose-dependent increase in response to ATP with a 50% effective concentration (EC50) of 16.7 microM. This reaction was independent of external Ca2+, indicating the presence of an internal Ca2+ reservoir. Neither adenosine, alpha, beta-methylene-ATP, 3'-O-(4-benzoylbenzoyl)-ATP, ADP, nor UTP evoked this reaction, whereas 2-methylthio-ATP induced an increase of [Ca2+]i with an EC50 of 14.4 microM. Moreover, P2 antagonists, reactive blue 2 and suramin, and a phospholipase C inhibitor, U-73122, inhibited the ATP-induced [Ca2+]i increase. These findings indicate the presence of a P2Y purinoceptor on the globular substance. In addition, granular fluorescence was observed in the quinacrine-stained macular sensory epithelium, indicating the presence of ATP-containing granules in this tissue. These results suggest that a paracrine mechanism involving ATP may exist in the macula and that this mechanism regulates the biological behavior of the globular substance.
Suzuki
H
H
Department of Otolaryngology, Tohoku University School of Medicine, Sendai, Japan.
Ikeda
K
K
Furukawa
M
M
Takasaka
T
T
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D006168:Guinea Pigs; D007700:Kinetics; D010037:Otolithic Membrane / Q000187:drug effects / Q000502:physiology*; D016716:PC12 Cells; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D012444:Saccule and Utricle; D013498:Suramin / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D014544:Uridine Triphosphate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D004963:Estrenes; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D011760:Pyrrolidinones; D018048:Receptors, Purinergic P2; D014227:Triazines; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C074854:U 73343; C012842:Cibacron Blue F 3GA; D013498:Suramin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D010738:Type C Phospholipases; D002118:Calcium; D014544:Uridine Triphosphate