Effects of Protein Kinase C on the Na+-H+ Exchange in the Cochlear Outer Hair Cell

Abstract

Dteda K, Suoose H, Takasaka T. Effect of protein kinase C on the Na ⁺ -H⁺ exchange in the cochlear outer hair cell. Acta Otolaryngol (Stockh) 1996; 116: 828-832.

Two routes, associated with protein kinase C (PKC) and cyclic AMP (cAMP), to regulate the activation of Na-H exchange (NHE) were investigated in the outer hair cell (OHC). the intracellular pH (pH) of OHC loaded with the pH indicator dye was measured by using fluorescence ratio imaging microscopy. the acid load was carried out by an “NH₄C1 pre-pulse”. the rate of acid extrusion after an acid load was increased as pH₁ became more acidic. the linear relationship between the rate of acid extrusion and pH; suggests the presence of an internal modifier site for the H⁺ ion on the NHE. Although addition of phorbol 12-myristate 13-acetate (TPA) had no effect on pH_j in unstimulated conditions, the pH, recovery from an acid load was enhanced by exposure to TPA. This finding can be explained by the pH < dependence of the PKC action, namely, that the activating effect of PKC on the NHE is facilitated by internal acidification. in contrast to the PKC effect, addition of dibutyryl cAMP failed to change the rate of acid extrusion. These findings are consistent with the characteristic property of the NHE-1. Thus, intracellular signal transduction to regulate the activity of the NHE in the OHC involves phosphorylation by PKC.

Key Words:

• cyclic AMP
• intracellular pH
• Na⁺-H⁺ exchange
• phosphorylation
• protein kinase C