ISSN:
1432-2013
Keywords:
Calcium channel blockers
;
Cytosolic calcium
;
Sodium pump
;
Muscle fibres
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
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 10−5M, 10−5M 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 Ca2+-induced inhibition of electrogenic pump, prevented by 10−5 M verapamil, 10−5M diltiazem and 10−7 M flunarizine. The results suggest that substances which block Ca2+ entry into the cell prevent the Ca2+ induced inhibition of the Na+ pump.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373994
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