Electrophysiological and morphological study of endolymphatic sac

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(Electrophysiological Study) The whole cell currents were measured in freshly isolated epithelial cells from the intermediate portion of the endolymphatic sac (ES) in the guinea pig by patch clamp technique. In most cells the outwardly delayd rectifying current was evoked by depolarizing voltage pulses. The reversal potential of the current was close to the potassium equilibrium potential, indicating that the outward current is carried mostly by potassium. The results suggest that the delayd rectifying current may play an important role in the potassium ion transport in the epithelial cells of the ES.(Morphological Study) 1) To investigate the detailed absorption activity and the barrier properties of the ES,a constant volume of horseradish peroxidase (HRP) aws injected directly into the ES lumen of the guinea pig. The epithelial cells in the proximal portion did not absorb the intraluminal HRP at any intervals after the tracer injection. The epithelial cells of the intermediate portion were classified clearly into two types according to their sbsortion activity : active-abosorptive and non-active cells. The absorption activity in the distal portion was lower than that in the active-absorptive cells in the intermediate portion. The epithelial linings of the ES showed a tight barrier to HRP.2) All epithelial cells in the distal portion and about a half the epithelial cells of the intermediate portion stained for carbonic anhydrase (CA). The proximal portion of the ES lacked immunoreactivity. The results suggest that CA may play a crucial role inthe electrolyte transport of the ES.