Chronic stimulation of acetylcholine receptors: differential effects on Na,K-ATPase isoforms in a myogenic cell line.

The myogenic cell line, C2C12, expresses two isoforms of the Na,K-ATPase catalytic subunit (alpha 1 and alpha 2) following differentiation. Hyperpolarization in myotubes following long-term exposure to carbachol (Henning et al. (1993) Br. J. Pharmacol., 111:459-464) suggests that the activity of one or both of the isoforms is increased after chronic stimulation of the acetylcholine receptor. We have examined explicitly the abundance of the two isoforms following such an exposure. Immunoblotting with specific antibodies did not detect any changes in the abundance of the alpha 1 isoform after a 3-day exposure to carbachol (10 microM). In contrast, there was a 50% increase in the abundance of alpha 2. These results suggest that chronic stimulation of the acetylcholine receptor produced a differential effect on the abundance of the alpha isoforms.