Effects of nifedipine and EGTA on endocochlear potential in the guinea pig.

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The endocochlear potential (EP) was measured in guinea pigs given calcium channel blockers and calcium chelating agents. The test solutions were administered either intravenously or by perilymphatic perfusion.Blood pressure was monitored during the intravenous infusion of nifedipine. The EP was decreased by intravenous nifedipine. The systemic blood pressure decreased immediately when 1mg/kg of nifedipine was given and the EP started to fall after about 30 sec. While 0.1mg/kg of nifedipine was being infused, the EP remained nearly unchanged until the blood pressure decreased irreversibly. With 0.01mg/kg, neither the blood pressure nor the EP showed any detectable change. It was concluded that the decrease of EP during the intravenous administration of nifedipine is secondary to its hypotensive action.During perilymphatic perfusion of nifedipine the EP fell from +70mV to +54mV and then returned to the initial level when the control solution without nifedipine was perfused again.EGTA, in a concentration of 10mM decreased the EP but only transiently, and there was a prompt return to the control level. EDTA in a concentration of 4mM had no significant effect on the EP. These results suggest that Ca ions play a role in maintaining the EP.
耳鼻咽喉科臨床学会の論文