P2X receptors in cochlear Deiters' cells

Abstract

1. The ionotropic purinoceptors in isolated Deiters' cells of guinea-pig cochlea were characterized by use of the whole-cell variant of the patch-clamp technique.

2. Extracellular application of adenosine 5′-triphosphate (ATP) induced a dose-dependent inward current when the cells were voltage-clamped at −80 mV. The ATP-induced current showed desensitization and had a reversal potential around −4 mV.

3. Increasing intracellular free Ca²⁺ by decreasing the concentration of EGTA in the pipette solution reduced the amplitude of the ATP-gated current.

4. The order of agonist potency was: 2-methylthioATP (2-meSATP)>ATP>benzoylbenzoyl-ATP (BzATP)>α,β-methyleneATP (α,β,meATP>adenosine 5′-diphosphate (ADP)>uridine 5′-triphosphate (UTP)>adenosine 5′-monophosphate (AMP)=adenosine (Ad).

5. Pretreatment with forskolin (10 μM), 8-bromoadenosine-3′,5′-cyclophosphate (8-Br-cyclic AMP, 1 mM), 3-isobutyl-1-methylxanthine (IBMX, 1 mM) or phorbol-12-myristate-13-acetate (PMA, 1 μM) reversibly reduced the ATP-induced peak current.

6. The results are consistent with molecular biological data which indicate that P2X₂ purinoceptors are present in Deiters' cells. In addition, the reduction of the ATP-gated current by activators of protein kinase A and protein kinase C indicates that these P2X₂ purinoceptors can be functionally modulated by receptor phosphorylation.

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