Objective: To measure the effects of neuro-active substances on intracellular free Ca2+ concentration ([Ca2+]i) in isolated outer hair cells(OHCs) of the guinea pig cochlea.
Methods: The fura-2 microfluorimetry was used to measure changes of [Ca2+]i in OHCs of the guinea pig cochlea after application of acetylcholine, ATP and carbacholine.
Results: Acetylcholine, ATP and carbacholine increased [Ca2+]i (acetylcholine: 0.74 +/- 0.12 mumol/L, ATP: 0.65 +/- 0.11 mumol/L, carbacholine: 1.16 +/- 0.27 mumol/L) in OHCs in the presence of extracellular Ca2+. In the absence of extracellular Ca2+, however, only ATP induced a gradual and small [Ca2+]i elevation, whereas other substances did not.
Conclusion: Acetylcholine and carbacholine, the cholinergic mascarinic agonists, increased [Ca2+]i in OHCs by acting at receptor-induced ion channel resulting in Ca2+ efflux. ATP-induced elevation of [Ca2+]i without Ca2+ in extracellular medium is due to a release of Ca2+ from an intracellular reservoir.