Ca(2+)-dependent regulation of the Ca(2+) concentration in the myometrium mitochondria. I. Trifluoperazine effects on mitochondria membranes polarization and [Ca(2+)](m)

摘要

Саsup2+/sup-dependent regulation of Casup2+/sup exchange in mitochondria is carried out with participation of calmodulin. We have shown previously that calmodulin antagonists reduced the level of mitochondrial membrane polarization and induced increase of the ionized Са concentration in both the mitochondrial matrix and cell cytoplasm. The concentration-dependent influence of trifluoperazine on the level of polarization of mitochondrial membranes has been shown in this work. The coordinates of the Hill graphs were used to calculate the constant K sub0.5/sub and the Hill coefficient. K sub0.5/sub was 24.4 ± 5 μM ( n = 10). The Hill coefficient was 2.0 ± 0.2, indicating the presence of two centers of the trifluoperazine binding. We have also studied [Casup2+/sup]subm/sub changes, when incubating mitochondria in mediums of different composition: without ATP and ions of Mg (0-medium), in the presence of 3 mM Mg (Mg-medium) and 3 mM Mg + 3 mM ATP (Mg,ATP-medium). It was shown that the composition of the incubation medium affected the [Casup2+/sup]subm/sub values in the absence of exogenous Casup2+/sup and did not affect them in the presence of the latter. Preincubation of mitochondria in mediums of different composition with 25 μM trifluoperazine did not affect the [Casup2+/sup]subm/sub values both before and after the addition of 100 μМ Саsup2+/sup to the incubation medium. It was concluded, that trifluoperazine depolarized myometrial mitochondria membranes in concentration-dependent manner. However, mitochondria preincubation with 25 μM trifluoperazine accompanied by 50% decrease in membrane polarization did not affect the [Casup2+/sup]subm/sub values.