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Tunicamycin reduces Na + ‐K + ‐pump expression in cultured skeletal muscle
Author(s) -
Alboim Sandra V.,
Bak Asia,
Sampson Sanford R.
Publication year - 1992
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041500325
Subject(s) - tunicamycin , cycloheximide , ouabain , diaphragm pump , myogenesis , skeletal muscle , tetraethylammonium chloride , biophysics , hyperpolarization (physics) , chemistry , intracellular , membrane potential , medicine , ionomycin , endocrinology , biology , biochemistry , protein biosynthesis , sodium , potassium , endoplasmic reticulum , stereochemistry , materials science , micropump , nuclear magnetic resonance spectroscopy , organic chemistry , unfolded protein response , nanotechnology
The purpose of this study was to examine effects of tunicamycin (TM), which inhibits core glycosylation of the β‐subunit, on functional expression of the Na + ‐K + pump in primary cultures of embryonic chick skeletal muscle. Measurements were made of specific‐[ 3 H]‐ouabain binding, ouabain‐sensitive 86 Rb uptake, resting membrane potential (E m ), and electrogenic pump contribution to E m (E p ) of single myotubes with intracellular microelectrodes. Growth of 4–6‐day‐old skeletal myotubes in the presence of TM (1 μg/ml) for 21–24 hr reduced the number of Na + ‐K + pumps to 60–90% of control. Na + ‐K + pump activity, the level of resting E m and E p were also reduced significantly by TM. In addition, TM completely blocked the hyperpolarization of E m induced in single myotubes by cooling to 10°C and then re‐warming to 37°C. Effects of tunicamycin were compared with those of tetrodotoxin (TTX; 2 x 10 −7 M for 24 hr), which blocks voltage‐dependent Na + channels. TM produced significantly greater decreases in ouabain‐binding and E m than did TTX, findings that indicate that reduced Na + ‐K + pump expression was not exclusively secondary to decreased intracellular Na + , the primary regulator of pump synthesis in cultured muscle. Similarly, effects of TM were significantly greater than those of cycloheximide, which inhibits protein synthesis by 95%. These findings demonstrated that effects were not due to inhibition of protein synthesis. We conclude that glycosylation of the Na + ‐K + pump β‐subunit is required for full physiological expression of pump activity in skeletal muscle.