Abstract
We investigated the effects of neomycin on nicotinic acetylcholine receptor-induced responses in bovine adrenal chromaffin cells. Neomycin inhibited the nicotinic agonist dimethylphenylpiperazinium iodide (DMPP)-induced norepinephrine secretion in a concentration-dependent manner. Neomycin had also an inhibitory effect on the DMPP-induced increase in cytosolic Ca++ concentration ([Ca++]i). This effect was further confirmed by inhibition of the DMPP-induced fluorescence quenching of fura-2 upon Mn++ entry. Under the same conditions, however, neomycin did not change the bradykinin-induced [Ca++]i increase, which follows the downstream signal of phospholipase C phospholipase C activation in this cell. The inhibitory effect of neomycin on the DMPP-induced [Ca++]i increase was apparent when the neomycin treatment was performed simultaneously with DMPP, suggesting a direct action on the nicotinic receptor. The direct inhibitory action of neomycin on the nicotinic receptor was also evident when neomycin inhibited the DMPP-induced cytosolic Ca++ increase, which is not affected by nifedipine nor ω-conotoxin MVIIC, and the cytosolic Na+ increase, which is not affected by tetrodotoxin. In addition, we observed that neomycin inhibited the binding of nicotine to the acetylcholine receptor in a noncompetitive manner. The data suggest that neomycin inhibits the nicotinic acetylcholine receptor directly, which results in blockage of the nicotinic receptor-mediated signaling without involvement of phospholipase C.
Footnotes
-
Send reprint requests to: Kyong-Tai Kim, Doctor of Philosophy, Department of Life Science, POSTECH, San 31, Hyoja Dong, Pohang, 790-784, Republic of Korea.
-
1 This work was supported by grants from the Hallym Academy of Sciences, Hallym University, the Korea Science, and Engineering Foundation (KOSEF 95-0401-02), and the Basic Science Research Institute Program (Project BSRI-96-4435) of the Ministry of Education.
- Abbreviations:
- DMPP
- dimethylphenylpiperazinium iodide
- InsP3
- inositol 1,4,5-trisphosphate
- [Ca++]i
- cytosolic calcium ion concentration
- [Na+]i
- cytosolic sodium ion concentration
- IC50
- half-maximal inhibitory concentration
- SBFI/AM
- sodium binding furan isophthalate tetraacetoxymethyl ester
- PLC
- phospholipase C
- PIP2
- phosphatidyl inositol 4,5-bisphosphate
- Received February 4, 1998.
- Accepted July 14, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|