Tunicamycin reduces Na+-K+-pump expression in cultured skeletal muscle

✍ Scribed by Sandra V. Alboim; Asia Bak; Sanford R. Sampson

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 844 KB
• Volume: 150
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041500325

✦ Synopsis

Abstract

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.