Calcium permeation of the turtle hair cell mechanotransducer channel and its relation to the composition of endolymph

被引:134
作者
Ricci, AJ [1 ]
Fettiplace, R [1 ]
机构
[1] Univ Wisconsin, Sch Med, Dept Neurophysiol, Madison, WI 53706 USA
来源
JOURNAL OF PHYSIOLOGY-LONDON | 1998年 / 506卷 / 01期
关键词
D O I
10.1111/j.1469-7793.1998.159bx.x
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
1. Recordings of mechanoelectrical transducer currents were combined with calcium imaging of hair bundles in turtle auditory hair cells located near the high-frequency end of the cochlea. The external face of the hair bundles was perfused with a range of Ca2+ concentrations to study the quantitative relationship between Ca2+ influx and transducer adaptation. 2. With Na+ as the monovalent ion, the peak amplitude of the transducer current decreased monotonically as the external [Ca2+] was raised from 25 mu M to 20 mM. When Na+ was replaced with the impermeant Tris the transducer current increased with external [Ca2+]. These results indicate that Ca2+ can both permeate and block the transducer channels. The Ca2+ concentration for half-block of the monovalent current was 1 mM. 3. To quantify the Ca2+ influx, the fraction of transducer current carried by Ca2+ was measured using the change in bundle fluorescence in cells loaded with 1 mM Calcium Green-1. The fluorescence change was calibrated by substituting an impermeable monovalent ion to render Ca2+ the sole charge carrier. 4. In the presence of Na+, the fractional Ca2+ current was similar to 10% in 50 mu M Ca2+, a concentration similar to that in endolymph, which bathes the hair bundles in vivo. The amount of Ca2+ entering was dependent on the identity of the monovalent ion, and was larger with K+, suggesting that the transducer channel is a multi-ion pore. 5. Over a range of ionic conditions, the rate of transducer adaptation was proportional to Ca2+ influx indicating that adaptation is driven by a rise in intracellular [Ca2+]. 6. Shifts in the current-displacement function along the displacement axis in different external Ca2+ concentrations were predictable from variation in the resting Ca2+ influx. We suggest that changes in the resting open probability of the transducer channels adjust the entry of Ca2+ to keep its concentration constant at an internal site. 7. The results demonstrate that endolymph containing high K+, 50 Ic nl Ca2+ and low Mg2+ concentrations, maximizes the transducer current while still allowing sufficient Ca2+ entry to drive adaptation. The hair cell mechanotransducer channel, in its permeation and block by Ca2+, shows behaviour similar to the voltage-gated Ca2+ channel and the cyclic nucleotide-gated channel.
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页码:159 / 173
页数:15
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