Regulation of ionized calcium concentration in mitochondria matrix in the absence of exogenous Са(2+)

Abstract

Functional activity of mitochondria depends on ionized calcium content in its matrix. Thus, investigation of the ways to influence Ca2+ transport and accumulation in these organelles is an urgent issue. The aim of this work was to evaluate ionized calcium concentration in the mitochondria matrix in the absence of exoge­nous Ca2+ and in the presence of Mg2+ and ATP in incubation media. The concentration of ionized calcium in mitochondria isolated from the myometrium of non-pregnant rats was measured with the fluorescent probe Fluo-4 AM, mitochondria hydrodynamic diameter was assessed using dynamic light scattering. The ATP concentration-dependent increase in ionized calcium concentration in mitochondria matrix in the absence of exogenous Са2+ and the high level of the total Са2+ accumulation after further addition of exogenous Са2+ were registered. The effect of ATP on Са2+ concentration did not depend on the blockage of mitochondrial PTP with cyclosporine A or on H+-ATPase/ATP-synthase inhibition with oligomycin, instead the addition of 10mM theophylline and 30 mM NaHCO3 to the Mg2+-containing medium led to Са2+ concentration elevation in mitochondria matrix. It was shown that low Ca2+ concentration in the matrix correlated with the increase in mitochondria size, whereas high Ca2+ concentration correlated with relatively smaller size of the organelles. Activation of the soluble adenylyl cyclase by NaHCO3 with simultaneous inhibition of phosphodiesterase by theophylline was accompanied by the decline in Са2+ probe normalized fluorescence in mitochondria matrix under conditions of exogenous Ca2+ introduction. It was suggested that the soluble adenylyl cyclase may be involved in regulation of Са2+ concentration in mitochondria matrix.

Keywords

• adenylyl cyclase
• fluo-4
• mitochondria matrix
• са(2+)