| Summary: | 碩士 === 中山醫學大學 === 醫學研究所 === 91 === Abstract
The effect of L-arginine on the mammalian cochlear outer hair cell was studied in this experiment. L-arginine but not D-arginine or other amino acids (L-aspartate or L-glutamine) induced length increases of guinea pig outer hair cell. Similarity, a membrane permeable cyclic GMP analog, 8-(-4- chloro- phenylthio) guanosine 3’，5’-cyclic monophosphate (pCPT -cGMP) or 8-bromo-guanosine 3’，5’-cyclic monopho- sphate induced length increases of guinea pig outer hair cells. These length increases induced by L-arginine can be attenuated by a 30 min preincubation of the cells with the nitric oxide synthase inhibitors, NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) or 7-nitroindazole (7-NINA). Comparison on the elongate effect of cell length of L-arginine and ionomycin, L-arginine did not change the fluorescence intensity of fluo-3. Preincubation of the cells with EGTA (3 mM) for 40 min to reduce the extracellular calcium concentration did not influence the effect of L-arginine. The results demonstrated that nitric oxide/cGMP pathway involved in regulating the slow motility of mammalian outer hair cell can not be ruled out.In addition, the effect of L-arginine is independent of extracellular calcium concentration.
Taicatoxin isolated from the venom of the Australian taipan snake (Oxyuranus scutellatus), has been previously regarded as a blockers of high threshold Ca2+ channels and small conductance Ca2+-activated K+ channels. Taicatoxin (0.19 mM) significantly prevented the cell shortening induced by high potassium (50 mM) medium. Similarly, cobaltous chloride, a nonselective calcium channel blocker, was to significantly reduced the effect of cell shortening induced by high potassium but not the effect of cell elongation induced by ionomycin. Other calcium channel blockers, nifedipine, w-conotoxin GVIA, w -agatoxin IVA did no such effect in prevented the cell length change induced by high potassium. Comparing the effects of taicatoxin and cobaltous chloride on the cell length and intracellular calcium change in outer hair cell, both taicatoxin and cobaltous chloride were able to prevent the cell shortening induced by high potassium but taicatoxin did not prevent the intracellular calcium increase induced by high calcium medium. The effect of taicatoxin was no relative with the membrane calcium channels or intracellular calcium concentration. In summary, the effects of L-arginine and taicatoxin were not relative with the calcium channels or cellular calcium concentration.
Neither the action of L-arginine, nor taicatoxin were relative with the changes of calcium concentration or calcium channels. These findings support the hypothesis of calcium-independent slow motility of outer hair cells as described previously.
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