Regulation of the sodium‐potassium pump in cultured rat skeletal myotubes by intracellular sodium ions

Abstract

The properties of the Na-K pump and some of the factors controlling its amount and function were studied in rat myotubes in culture. The number of Na-K pump sites was quantified by measuring the amount of [3H]ouabain bound to whole-cell preparations. Activity of the pump was determined by measurement of ouabain-sensitive 86Rb-uptake and component of membrane potential. Chronic treatment of myotubes with tetrodotoxin (TTX), which lowers [Na]i, decreased the number of Na-K pumps, the ouabain-sensitive 86Rb uptake, and the size of the electrogenic pump component of Em. In contrast, chronic treatment with either ouabain or veratridine, which increases [Na+]i, resulted in an elevated level of Na-K pump sites. This effect was blocked by inhibitors of protein synthesis. Neither rates of degradation nor affinity of pump sites in cells treated with TTX, veratridine, or ouabain differred from those in control cells. The number and activity of Na-K pump sites were unaffected by chronic elevation in [Ca]i or chronic depolarization. We conclude that alterations in the level in intracellular Na ions play the major role in regulation of Na-K pump synthesis in cultured mammalian skeletal muscle.

Evidence for coordinate regulation of the A system for amino acid transport and the mRNA for the alpha 1 subunit of the Na+,K(+)-ATPase gene in Chinese hamster ovary cells.

“…K+ levels were not significantly altered after cells were starved. These observations do not support the concept suggested by others (27,31) that induction of Na+,K+-ATPase gene expression might be triggered by increases in intracellular Na+ levels. Our experiments show that there was a significant increase in abundance of the mRNA for the Na+,K+-ATPase a1-subunit gene when cells were starved, even in the presence of low intracellular Na+ levels.…”

“…Besides the concentration of Na' affecting the activity of the Na',K+-ATPase, under certain conditions that lead to increases in Na+ content there is an associated increase in the number of Na+,K+-ATPase molecules on the plasma membrane (16,(23)(24)(25)(26)(27)(28)(29)(30) and an increase in the abundance of their corresponding mRNA (29,30). This has led to the idea that the Na' concentration itself may have a pretranslational effect resulting in these reported increases (27,31).…”

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

“…This effect was not statistically significant (P > 0.05) (see, however, Brodie and Sampson, 1989a). In contrast, TM caused a decrease in specific ouabain binding of 48% (P < 0.001) compared with control myotubes.…”

The glial voltage-gated sodium channel: cell- and tissue-specific mRNA expression.

“…The arguments that (i) Na-G is apparently the only Na-channel mRNA species expressed in Schwann cells and (ii) Na currents in Schwann cells in vivo (19) are about 2 orders less sensitive to TTX than nodal Na currents (1) plead against it. More probable seems the implication of the Na-G-type Na channels in some general cellular functions such as the regulation of resting potential and ion homeostasis, possibly via regulation of Na,KATPase, whose activity is highly dependent on intracellular Na+ concentration (44). Finally, by creating local depolarizations, the activation of small numbers of Na channels in nonexcitable cells may lead to activation of other voltagesensitive ionic channels (e.g., K+ and Ca2+ channels) and may thus be an early step in a cascade ofmetabolic reactions.…”