Decrease in the electrogenic Contribution of Na,K-ATPase and the resting membrane potential as a possible mechanism of Ca2+ accumulation in rat soleus muscle in a short-term gravity unloading

Autor: E. G. Altaeva, E. E. Nikol’sky, Boris Shenkman, V. V. Kravtsova, T. M. Drabkina, Prokof'ev Av, I. V. Kubasov, Igor I. Krivoi
Rok vydání: 2008
Předmět:
Zdroj: Biophysics. 53:586-591
ISSN: 1555-6654
0006-3509
DOI: 10.1134/s0006350908060225
Popis: The resting membrane potential and electrogenic contribution of α1- and α2-isoforms of Na+/K+-ATPase in the rat soleus muscle at early stages of gravity unloading were analyzed. The role of L-type calcium channels in accumulation of calcium ions in the myoplasm under these conditions was estimated. After 3-day antiorthostatic suspension, the resting membrane potential of the muscle fibers decreased from −71.0 ± 0.5 to −66.8 ± 0.7 mV, the muscle excitability reduced, and a trend of muscle fatigue acceleration appeared. The electrogenic contribution of ouabain-sensitive α2-isoform of Na+/K+-ATPase, determined as the depolarization caused by 1μM ouabain, decreased after suspension from 6.2 ± 0.6 to 0.5 ± 0.8 mV. The contribution of ouabain-resistant α1-isoform of Na+/K+-ATPase, determined as an additional depolarization after addition of 500 μM ouabain, decreased from 4.6 ± 0.6 to 2.6 ± 0.6 mV. The intensity of Fluo-4AM fluorescence in individual muscle fibers increased after suspension more than fourfold, which suggests an elevated calcium concentration in the myoplasm. A local delivery of nifedipine, a blocker of the L-type calcium channels, to the muscle removed this effect. The existence of a selective mechanism suppressing the electrogenic contribution of Na+/K+-ATPase α2-isoform, which is the main cause of the muscle fiber membrane depolarization after 3-day suspension, is postulated. The depolarization can activate part of potential-sensitive L-type Ca2+ channels, causing the accumulation of calcium ions in the muscle fiber myoplasm.
Databáze: OpenAIRE
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