MITOCHONDRIAL CONTACT SITES DETECTED BY CREATINE-PHOSPHOKINASE ACTIVITY IN THE HEARTS OF NORMAL AND DIABETIC RATS - IS MITOCHONDRIAL CONTACT SITES FORMATION A CALCIUM-DEPENDENT PROCESS
B. Ziegelhoffermihalovicova et al., MITOCHONDRIAL CONTACT SITES DETECTED BY CREATINE-PHOSPHOKINASE ACTIVITY IN THE HEARTS OF NORMAL AND DIABETIC RATS - IS MITOCHONDRIAL CONTACT SITES FORMATION A CALCIUM-DEPENDENT PROCESS, General physiology and biophysics, 16(4), 1997, pp. 329-338
Mitochondrial contact sites (MiCS) are structures in the mitochondrial
membrane containing the structure-bound mitochondrial isoenzyme of cr
eatine phosphokinase that participates in the transfer of energy into
the cytoplasm. This explains the increased formation of MiCS found in
hearts with high metabolic activity. Earlier we demonstrated that enha
nced MiCS formation may also be induced by perfusing the heart with in
creased, but still not cardiodepressive concentrations of Ca2+ (2.2 mm
ol.l(-1)) in the perfusate. Nevertheless, neither the molecular mechan
ism by which Ca2+ ions may induce an increase in MiCS formation, nor t
he dependence of Ca2+-induced MiCS formation on the intracellular Ca2 level have yet been elucidated. In the present study we investigated
the effect of Langendorff-perfusion with 2.2 mmol.l(-1) Ca2+ on format
ion of MiCS in normal as well as in diabetic hearts. The latter, namel
y, are characterized by altered metabolism as well as Ca2+-handling, r
esulting in elevated [Ca2+](i). We have found that the amounts of MiCS
in diabetic hearts outnumbered those in normal hearts. Our results sh
owed that in comparison to perfusion with 1.6 mmol.l(-1) Ca2+ a perfus
ion with 2.2 mmol.l(-1) Ca2+ is capable of significantly increasing (p
< 0.01) the formation of MiCS in control hearts. In both groups of di
abetic hearts the numbers of MiCS were significantly increased in comp
arison to healthy controls (p < 0.01). Moreover, no significant differ
ences in amounts of MiCS were found between healthy hearts perfused wi
th 2.2 mmol.l(-1) Ca2+ and diabetic hearts of both groups (p > 0.05).
In diabetic hearts, MiCS formation in response to [Ca2+](e) was little
manifested. Our results also confirmed that elevated [Ca2+](i) in all
cases represented a signal for increased formation of MiCS in the hea
rt.