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The effects of calcium and calcium channel blockers on sodium pump
T Stankovicová1, H Zemková, A Breier
1Faculty of Pharmacy, Department of Pharmacology and Toxicology, Bratislava, Slovak Republic.
Abstract:
The effects of 10 mM Ca2+ and Ca2+ channel blockers verapamil, diltiazem and flunarizine on the ouabain-sensitive electrogenic Na+, K+ pump activity of mouse diaphragm muscle fibres enriched with Na+ were compared with the changes in cytosolic [Ca2+]. The electrogenic Na+ pump activity produced by adding K+ to muscles previously bathed for 4 h in a K(+)-free, 2-mM [Ca2+] solution increased the resting membrane potential by about 18 mV. This hyperpolarization was completely inhibited after 10 min incubation in 10 mM Ca2+. Verapamil 10(-5) M, 10(-5) M diltiazem and 10(-7) M flunarizine effectively prevented the effect of elevated [Ca2+]. At these concentrations, these drugs did not affect the K(+)-induced hyperpolarization. In mouse diaphragm, the basal cytosolic [Ca2+] measured by the fluorescent indicator 1-[2-(5-carboxyoxazol-2-yl)-6- aminobenzofuran-5-oxy]2-(2'-amino-5'-methylphenoxy)ethane-N,N,N',N '- tetraacetic acid acetoxymethyl ester (fura-2/AM) was 261 +/- 6 nM. After 4 h in a Liley K(+)-free, 2 mM [Ca2+] solution, the cytosolic [Ca2+] increased to 314 +/- 28 nM. Increase in [Ca2+] from 2 to 10 mM caused a twofold increase of cytosolic [Ca2+] to 637 +/- 26 nM. This rise was, like the Ca(2+)-induced inhibition of electrogenic pump, prevented by 10(-5) M verapamil, 10(-5) M diltiazem and 10(-7) M flunarizine. The results suggest that substances which block Ca2+ entry into the cell prevent the Ca(2+)-induced inhibition of the Na+ pump.
Insights
High extracellular calcium inhibits the Na+, K+ pump in mouse diaphragm muscle cells. Calcium channel blockers like verapamil, diltiazem, and flunarizine prevent this inhibition by blocking calcium entry.
Area of Science:
- Cell Physiology
- Ion Transport
- Muscle Electrophysiology
Background:
- The Na+, K+ pump is crucial for maintaining cellular ion balance and membrane potential.
- Elevated extracellular calcium ([Ca2+]) can affect cellular functions, including ion transport.
- Understanding the regulation of the Na+, K+ pump by [Ca2+] is important for muscle physiology.
Purpose of the Study:
- To investigate the impact of high extracellular calcium on the electrogenic Na+, K+ pump activity in mouse diaphragm muscle fibers.
- To determine if calcium channel blockers can prevent the inhibitory effects of elevated [Ca2+] on the Na+, K+ pump.
- To correlate changes in cytosolic calcium ([Ca2+]) with Na+, K+ pump activity.
Main Methods:
- Measurement of electrogenic Na+, K+ pump activity via K+-induced hyperpolarization in mouse diaphragm muscle fibers.
- Manipulation of extracellular calcium concentrations (2 mM to 10 mM).
- Application of calcium channel blockers: verapamil, diltiazem, and flunarizine.
- Measurement of cytosolic [Ca2+] using the fluorescent indicator fura-2/AM.
Main Results:
- High extracellular calcium (10 mM) completely inhibited the Na+, K+ pump activity.
- Verapamil, diltiazem, and flunarizine prevented the Ca2+-induced inhibition of the Na+, K+ pump at specific concentrations.
- Elevated extracellular calcium led to a significant increase in cytosolic [Ca2+], which was also attenuated by the calcium channel blockers.
- The tested calcium channel blockers did not affect basal K+-induced hyperpolarization.
Conclusions:
- Extracellular calcium influx inhibits the electrogenic Na+, K+ pump in mouse diaphragm muscle.
- Calcium channel blockers effectively prevent the Ca2+-induced inhibition of the Na+, K+ pump by reducing calcium entry.
- These findings highlight the role of calcium signaling in regulating Na+, K+ pump function in muscle cells.