蝸牛外リンパの定量的生化学

抄録

The influence of cerebrospinal fluid (CSF) to perilymph composition in the scala tympani of the cochlea, and the difference of transport mechanism of organic anions between scala tympani and scala vestibuli ware studied to elucidate the metallic elements in the perilymph measured with a new method-an inductively-coupled plasma atomic emission spectrometer. And the effect of acoustic overstimulation and anoxia on the concentrations of these metallic elements was investigated.
Results and conclusions were as follows:
1) Samples of less than 200nl taken through the round window showed relatively high glycine and alanine contents, comparable to the level found in the scala vestibuli. If a larger amount was withdrawn, lower glycine or alanine levels were observed. This is consistant with CSF which has low glycine and alanine drawn into the scala tympani through the cochlear aqueduct and contaminating the sample.
2) To investigate the transport mechanism of organic anions from blood to perilymph, the concentrations of furosemide, penicillin G and salicylate in the perilymph of the scala tympani (STP) and the scala vestibuli (SVP) were measured after intravenous administrations of these drugs. The steep gradient of furosemide and penicillin G concentrations between STP and the serum was maintained for 2 hours after administration. The maximum concentrations were observed in STP at 15min for furosemide and at 60min for penicillin G, though no elimination was observed in SVP at least for 2 hours. Moreover, high dosage of the competitive inhibitor for organic anion transport, probenecid or sulfinpyrazone, had a drastic effect on the elimination of furosemide or penicillin G in STP, i. e. the concentration in STP increased slowly for 2 hours without any elimination in animals with pretreatment of probenecid or sulfinpyrazone, which had no effect on the elimination in SVP. These results suggested a difference in the transport mechanism of furosemide and penicillin G between STP (active transport) and SVP (passive transport). On the contrary, there was no difference in the elimination of salicylate between STP and SVP.
3) The concentrations of phosphorus and eight metallic elements, i. e. calcium, copper, iron, potassium, magnesium, sodium, lead and zinc were measured simultaneously in a 2μl sample of STP. Our study is the first report on the quantitative measurement of copper, iron, lead and zinc in STP. There was no significant effect of acoustic overstimulation on the concentrations of these elements except for magnesium, which decreased significantly after the exposure to a intense sound (2kHz, 115 dBSPL) for 15min. Among these cationic elements, only iron significantly increased at 5min after anoxia (for 3min) and decreased thereafter to the steady state level in 30min. These rapid changes of iron concentration in STP after the anoxia are very interesting with respect to free radicals, though detailed mechanisms are yet to be clarified. Further biochemical, physiological and morphological studies are necessary to elucidate the roles of these metallic elements in cochlear function.