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

• Published in: Ukrains'kyi biokhimichnyi zhurnal (1999 ) Vol. 76; no. 5; p. 52
• Main Authors: Babich, L G, Borisova, L A, Shlykov, S G, Titus, O V, Kosterin, S A
• Format: Journal Article
• Language: Russian
• Published: Ukraine 01.09.2004
• Subjects: Adenosine Triphosphate - metabolism; Animals; Biological Transport - drug effects; Calcium - metabolism; Cells, Cultured; Female; Kinetics; Magnesium Chloride - pharmacology; Mitochondria - drug effects; Mitochondria - metabolism; Myocytes, Smooth Muscle - cytology; Myocytes, Smooth Muscle - drug effects; Myocytes, Smooth Muscle - metabolism; Myometrium - cytology; Myometrium - drug effects; Myometrium - metabolism; Organelles - drug effects; Organelles - enzymology; Rats; Sarcoplasmic Reticulum - drug effects; Sarcoplasmic Reticulum - enzymology; Spermine - pharmacology

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.