Extracellular ATP-induced Ca2+ mobilization of type I spiral ganglion cells from the guinea pig cochlea.
Intracellular calcium concentrations ([Ca2+]i) in type I cochlear spiral ganglion cells (SGCs) of the guinea pig were measured by digital imaging microscopy and the Ca(2+)-sensitive dye Fura-2. Extracellular ATP induced elevation of [Ca2+]i in type I SGCs in a concentration-dependent manner. The ATP-induced elevation of [Ca2+]i in SGC was even evident in the Ca(2+)-free solution, thereby suggesting that ATP induces a Ca(2+)-release from intracellular stores in SGCs. Suramin and reactive blue 2, both antagonists for the P2-purinergic receptor, inhibited the [Ca2+]i increase in SGCs induced by extracellular ATP in a dose-dependent manner. Adenosine did not induce any changes of [Ca2+]i in SGC. These results suggest that type I SGCs may possess P2-purinergic receptor but not P1-purinergic receptor. Extracellular ATP induced a [Ca2+]i increase in type I SGCs, with and without neuritic processes, while L-glutamate increased [Ca2+]i in type I SGCs with neuritic processes, but not SGCs without neuritic processes. The ATP-induced [Ca2+]i increase was almost equal in both soma and processes. Therefore, the distribution of P2-purinergic receptor in type I SGCs may be homogeneous in soma and processes. Based on these observations, we suggest that extracellular ATP may act as a neurotransmitter or neuromodulator of the hair cell-afferent nerve synapse in the guinea pig cochlea.
Cho
H
H
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Harada
N
N
Yamashita
T
T
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000032:analysis; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003051:Cochlea / Q000737:chemistry / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000737:chemistry; D005453:Fluorescence; D006168:Guinea Pigs; D009475:Neurons, Afferent; 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
D004791:Enzyme Inhibitors; D018048:Receptors, Purinergic P2; D014227:Triazines; C012842:Cibacron Blue F 3GA; D013498:Suramin; D000252:Calcium-Transporting ATPases; D000241:Adenosine; D002118:Calcium