[Inhibition of nifedipine on inward current of Hensen cell induced by ATP].
OBJECTIVE
To investigate the effect of nifedipine on the non-selective inward current of cochlear Hensen cell induced by ATP in high concentrations.


METHODS
The organ of Corti was treated using enzyme, and then dissociated mechanically to isolate Hensen cells. The whole cell patch-clamp technique was used to record ion currents in Hensen cells which had integrated border, round shape and translucent intracellular cytoplasm. Drugs were delivered to the cell by a micro-manifold consisting made by three 100 microm diameter microtubules, including 0.1 mmol/L ATP, 1 mmol/L ATP, 10 mmol/L ATP, 0.1 mmol/L ATP + 0. 1 mmol/L suramin (purinergic antagonist), stimulation of extracellular fluid alone, 140 mmol/L CsCl (replace KCL in intracellular fluid) + 1 mmol/L ATP, 40 mmol/L TEA (blocker of potassium channel) + 1 mmol/L ATP, and 1 mmol/L ATP + 10 micromol/L nifedipine, respectively.


RESULTS
When isolated Hensen cell was given 0.1 mmol/L (n = 10), 1 mmol/L (n = 10), 10 mmol/L( n = 6) ATP separately, an inward ion current could be recorded, which enhanced with increased ATP concentration and showed dose-dependence. Further study indicated that the inward ion current could be inhibited by 0.1 mmol/L suramin (n = 5), 140 mmol/L CsCl (n = 5) and 40 mmol/L TEA (n = 5). There was no ion current be recorded when the cell was stimulated with the extracellular fluid alone, neither inward nor outward. However, the inward ion current vanished and an outward ion current appeared instead, when 1 mmol/L ATP and 10 micromol/L nifedipine were given together (n = 5).


CONCLUSIONS
An inward current was evoked in isolated Hensen cell by ATP in high concentrations. This inward current seems to be associated closely with potassium channels without the participation of mechanical channels. Nifedipine can inhibit this inward current and induce an outward current, which is similar to the normal potassium current in isolated Hensen cell. It suggests that nifedipine have partly protective effect on the function of cochlea by inducing modulate of the potassium circle of cochlea in Hensen cell's tache.
Li
Xing-Qi
XQ
Institute of Otorhinolaryngology, General Hospital of Chinese People's Liberation Army, Beijing 100853, China. lixq@301hospital.com.cn
Li
Jian-Xiong
JX
Yu
Hong
H
Hou
Zhi-Qiang
ZQ
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D003051:Cochlea / Q000166:cytology; D005260:Female; D006168:Guinea Pigs; D007760:Labyrinth Supporting Cells / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects*
D024661:Potassium Channels, Inwardly Rectifying; D000255:Adenosine Triphosphate; D009543:Nifedipine