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.