Intracellular Calcium Changes by Hyposmotic Activation of Cochlear Outer Hair Cells in the Guinea Pig

Abstract

During continued exposure to a hypotonic solution, isolated outer hair cells (OHCs) from the guinea pig cochlea showed a regulatory volume decrease (RVD) after initial cell swelling. In the absence of extracellular Ca²⁺, RVD was significantly inhibited. Using Ca²⁺-sensitive dye fura-2, accompanying changes of the intracellular Ca²⁺ concentrations ([Ca²⁺]_i) of OHC were investigated. Hyposmotic activation resulted in a [Ca²⁺]_i increase associated with cell shortening and swelling. In a Ca²⁺ -free solution, [Ca²⁺]_i was not significantly increased during hyposmotic activation although shortening and swelling of the OHC was observed. These results suggest that the increase in [Ca²⁺]_i during hyposmotic activation is mainly based on an influx or extracellular Ca²⁺ which proceeds the RVD.

Key Words:

• regulatory volume decrease
• outer hair cell
• fura-2
• hyposmotic activation