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Calcium‐dependent regulation of phospholipase A 2 and its inhibitors, including tetracaine, for acetylcholine receptor cluster formation in mouse myotubes co‐cultured with spinal cord explant
Author(s) -
Kimura M.,
Kimura I.,
Shikada A.,
Takahashi K.
Publication year - 1987
Publication title -
international journal of developmental neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.761
H-Index - 88
eISSN - 1873-474X
pISSN - 0736-5748
DOI - 10.1016/0736-5748(87)90058-x
Subject(s) - tetracaine , chemistry , procaine , egta , acetylcholine receptor , acetylcholine , phospholipase a , calcium , medicine , endocrinology , phospholipase a2 , receptor , biochemistry , pharmacology , biology , enzyme , organic chemistry , neuroscience , lidocaine
Regulatory effects of phospholipase A 2 (PLA 2 ) on acetylcholine receptor (AChR) cluster formation were investigated in developing mouse myotubes co‐cultured with spinal cord explant, using quinacrine, cortisone, tetracaine and related agents. AChR was visualized using fluorescence‐conjugated α‐bungarotoxin. Peak fluorescence intensity and total fluorescence within the fluorescence stain were measured as indices of AChR cluster formation and AChR content, respectively. Both indices were gradually increased from day 9 to 13 in culture. PLA 2 (0.2–1.0 μg/ml), melittin (10 μg/ml) and arachidonic acid (100 μM), added to the culture medium from the second day, clearly inhibited both indices at days 11 and 13, whereas the addition of phospholipase C (1 μg/ml) inhibited peak fluorescence but did not affect total fluorescence. The co‐existence of PLA 2 with its inhibitors—quinacrine (3 μM), cortisone (0.01 μM) and tetracaine (30 μM)—significantly overcame the PLA 2 ‐induced inhibition of both indices. The elevation of calcium ion concentrations from 2.9 to 10 mM abolished the increase of both indices. Ouinacrine (10 μM), cortisone (0.1 μM) and tetracaine (100 μM) alone similarly inhibited both fluorescence indices. The addition of EGTA (2 mM) from day 8 overcame tetracaine‐induced inhibition but not quinacrine‐ or cortisone‐induced inhibition. These results suggest that the formation of AChR clusters in developing myotubes is negatively controlled by endogenous PLA 2 activity. This overcoming of PLA 2 ‐induced inhibition by tetracaine may be dependent on calcium ion mobilization, whereas that by quinacrine and cortisone may not.