Extracellular adenosine 5'-ATP-induced calcium signaling in isolated vestibular ganglion cells of the guinea pig.
Extracellular adenosine 5'-triphosphate (ATP)-induced intracellular calcium concentration ([Ca2+]i) changes in acutely isolated vestibular ganglion cells (VGCs) of the guinea pig were investigated using the Ca2+ -sensitive dye Fura-2. Extracellular ATP induced an increase in [Ca2+]i in VGCs in a dose-dependent manner. ATP induced an increase in [Ca2+]i even in the absence of extracellular Ca2+ (1 mM Ethylene Glycol-bis (beta-aminoethyl Ether) N,N,N',N'-Tetraacetic Acid (EGTA)), thus suggesting that ATP induces Ca2+ release from the intracellular stores. The P2-receptor antagonists suramin and reactive blue 2 inhibited the ATP-induced [Ca2+]i increase in a dose-dependent manner. The P1-receptor agonist adenosine did not induce any changes in [Ca2+]i. These results suggest that VGCs may possess a P2-purinergic receptor but not a P1-purinergic receptor. La3+, a receptor-mediated calcium channel blocker, inhibited the ATP-induced [Ca2+]i increase but, in contrast, nifedipine, a L-type calcium channel blocker, did not. These results suggest that ATP induces both a Ca2+ -release from the intracellular stores and a Ca2+ influx from the extracellular space through La3+ -sensitive and nifedipine-insensitive Ca2+ channels in VGCs. Our results also suggest that extracellular ATP may act as a neurotransmitter or neuromodulator of the vestibular peripheral system in the guinea pig.
Nagata
N
N
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Harada
N
N
Chen
L
L
Cho
H
H
Tomoda
K
K
Yamashita
T
T
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003051:Cochlea / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000737:chemistry / Q000187:drug effects; D005453:Fluorescence; D006168:Guinea Pigs; D006801:Humans; D007150:Immunohistochemistry; D009475:Neurons, Afferent / Q000187:drug effects / Q000201:enzymology; D009543:Nifedipine / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000187:drug effects; D013136:Spiral Ganglion / Q000737:chemistry / Q000166:cytology / Q000201:enzymology*; D013498:Suramin / Q000494:pharmacology; D013997:Time Factors; D014227:Triazines / Q000494:pharmacology; D014722:Vestibule, Labyrinth / Q000187:drug effects*
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D014227:Triazines; C012842:Cibacron Blue F 3GA; D013498:Suramin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D002118:Calcium