[Effect of Mg ions and spermine on ATP-dependent Ca2+ transport in myometrial intracellular structures. I. Comparative study of Ca2+ accumulation in mitochondria and sarcoplasmic reticulum].
In experiments, which were carried out with the use of a radioactive label (45Ca2+) on the suspension of rat uterus myocytes treated by digitonin solution (0.1 mg/ml), influence of Mg ions and spermine on Mg2+, ATP-dependent Ca2+ transport in mitochondria and sarcoplasmic reticulum was investigated. Ca2+ accumulation in mitochondria (1324 +/- 174 pmol Ca2+/10(6) cells for 1 min - the control) was tested as such which was not sensitive to thapsigargin (100 nM) and was blocked by ruthenium red (10 microM). Oxalate-stimulated Ca2+ accumulation in sarcoplasmic reticulum (136 +/- 17 pmol Ca2+/10(6) cells for 1 min - the control) was tested as such which was not sensitive to ruthenium red and was blocked by thapsigargin. It has been shown, that initial speed and level of energy-dependent Ca2+ accumulation in mitochondria considerably exceeded the values of these parameters for sarcoplasmic reticulum Ca2+-accumulation system. Ca2+ accumulation kinetic in mitochondria was characterized by a steady-state phase (for 5-10 min. of incubation) while accumulation kinetic of this cation in sarcoplasmic reticulum corresponded to zero order reaction. Increase of Mg2+ concentration up to 5 mM led to activation of Ca2+-accumulation systems in mitochondria and sarcoplasmic reticulum (values of activation constants K(Mg) for Mg2+ were 2.8 and 0.6 mM, accordingly). Concentration dependence of spermine action on Ca2+ accumulation in mitochondria was described by a dome-shaped curve with a maximum at 1 mM spermine. In case of sarcoplasmic reticulum Ca2+ pump only the inhibition phase was tested at spermine concentration above 1 mM. However values of inhibition constants for both transporting systems were practically identical--5.2 +/- 0.6 and 5.7 +/- 0.7 mM, accordingly. Hence, Mg ions carry out the important role in regulation of energy-dependent Ca2+ transporting systems both in uterus smooth muscle mitochondria and sarcoplasmic reticulum. Spermine acts first of all on mitochondrial calcium uniporter.
Babich
L G
LG
Borisova
L A
LA
Shlykov
S G
SG
Titus
O V
OV
Kosterin
S A
SA
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009215:Myometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015388:Organelles / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D013096:Spermine / Q000494:pharmacology*
D015636:Magnesium Chloride; D013096:Spermine; D000255:Adenosine Triphosphate; D002118:Calcium