Effects of Intracellular Calcium and Calcium Channel Blockers on Outer Hair Cells of Guinea Pig Cochlea

細胞內鈣離子與鈣離子管道對於天竺鼠耳蝸外毛細胞的影響

This study investigated calcium currents in isolated outer hair cells (OHC) of guinea pig cochlea using whole cell patch-clamp and intracellular calcium imaging. A P/Q-type Ca(superscript 2+) channel blocker ω-conotoxin MVIIC (5μM) similar to nifedipine (30μM) and Cd(superscript 2+) (1mM), inhibited both the Ca(superscript 2+) current and Ca(superscript 2+)-activated-K(superscript +)-current. The Ca(superscript 2+) current was inhibited by nifedipine. The residual amplitude was further reduced by the addition of 5μM ω-conotoxin MVIIC. According to our measurements of [Ca(superscript 2+)](subscript i), both nifedipine and ω-conotoxin MVIIC reduced the effect of [Ca(superscript 2+)](subscript i) induced by external application of the high K(superscript +) medium (50 mM). The shortening of OHC was induced by the application of the high K(superscript +) medium, while introduction calcium channel blockers or lowering the extracellular calcium concentration did not inhibit the hair cell shortening evoked by high K(superscript +) stimulation. It was concluded that the shortening of OHC induced by high K(superscript +) medium is independent on the extracellular Ca(superscript 2+), membrane Ca(superscript 2+) and Ca(superscript 2+)-activated K(superscript +)-channels. The possible mechanism underlying the unique property of outer hair cells is discussed.

我們使用細胞膜電位鉗定與鈣離子細胞影像分析研究天竺鼠內耳外毛細胞鈣離子電流的功能角色。海洋錐螺毒素ω-Conotoxin MVIIC（5μM）是一選擇性P／Q－型鈣離子管道阻斷劑與nifedipine（L－型，30μM）與鎘離子（非選擇型，1mM）相似，可抑制鈣離子電流與鈣離子活化型鉀電流。實驗中外毛細胞鈣電流可被nifedipine抑制一部份。而剩餘的部份可被ω-Conotoxin MVIIC（5μM）所抑制。依據細胞內鈣離子影像分析得知nifedipine和ω-Conotoxin MVIIC皆可抑制由高鉀溶液（50mM）引發的細胞內鈣離子上升作用。高鉀溶液可以縮短外毛細胞的長度，然而給予鈣離子管道抑制劑或降低細胞外液鈣離子濃度皆不能對抗高鉀所引發的毛細胞縮短的現象。總之，高鉀所引發的毛細胞縮短的現象與細胞外液鈣離子濃度，鈣離子管道本身與鈣離子活化的鉀管道無關。此外毛細胞獨特性質的機轉於此文章中討論。