Heterogeneity of ADP Diffusion and Regulation of Respiration in Cardiac Cells

Abstract

Heterogeneity of ADP diffusion and regulation of respiration were studied in permeabilized cardiomyocytes and cardiac fibers in situ and in silico. Regular arrangement of mitochondria in cells was altered by short-time treatment with trypsin and visualized by confocal microscopy. Manipulation of matrix volumes by changing K(+) and sucrose concentrations did not affect the affinity for ADP either in isolated heart mitochondria or in skinned fibers. Pyruvate kinase (PK)-phosphoenolpyruvate (PEP) were used to trap ADP generated in Ca,MgATPase reactions. Inhibition of respiration by PK-PEP increased 2-3 times after disorganization of regular mitochondrial arrangement in cells. ADP produced locally in the mitochondrial creatine kinase reaction was not accessible to PK-PEP in intact permeabilized fibers, but some part of it was released from mitochondria after short proteolysis due to increased permeability of outer mitochondrial membrane. In in silico studies we show by mathematical modeling that these results can be explained by heterogeneity of ADP diffusion due to its restrictions at the outer mitochondrial membrane and in close areas, which is changed after proteolysis. Localized restrictions and heterogeneity of ADP diffusion demonstrate the importance of mitochondrial functional complexes with sarcoplasmic reticulum and myofibrillar structures and creatine kinase in regulation of oxidative phosphorylation.

Mitochondrial regular arrangement in muscle cells: a “crystal-like” pattern

“…Similarly, in ischemic hearts, various alterations in mitochondrial function such as the significant decrease in maximal respiration rate and half-saturation constant for ADP were observed in parallel with the changes in structural organization of the cardiac muscle cells (7,16). These experimental results suggest that there is a direct link between regulation of muscle cell energetics and structural organization of the cell (28).…”

“…In addition, kinetic studies have shown a direct supply of endogenous ADP from ATPases to mitochondria (30,34). Such interaction can be explained by the existence of localized intracellular diffusion restrictions (28,39). A mild treatment of the fibers with trypsin leads to the removal of these diffusion restrictions, and at the same time, distribution of mitochondria in the fiber is changed from regular arrangement in the control to random distribution after the treatment (28).…”

“…Such interaction can be explained by the existence of localized intracellular diffusion restrictions (28,39). A mild treatment of the fibers with trypsin leads to the removal of these diffusion restrictions, and at the same time, distribution of mitochondria in the fiber is changed from regular arrangement in the control to random distribution after the treatment (28). Similarly, in ischemic hearts, various alterations in mitochondrial function such as the significant decrease in maximal respiration rate and half-saturation constant for ADP were observed in parallel with the changes in structural organization of the cardiac muscle cells (7,16).…”

Does intracellular metabolite diffusion limit post-contractile recovery in burst locomotor muscle?

“…These are likely to include systems with relatively high rates of ATP production/consumption and distant sites of ATP utilization, such as in some muscle fibers with a higher aerobic capacity than examined here (Meyer et al, 1984;Stokes and Josephson, 1992;Vendelin et al, 2000;Saks et al, 2003;Suarez, 2003) or in the flagellum of spermatozoa, which has been the subject of many reaction-diffusion analyses (e.g. Nevo and Rikmenspoel, 1969;Tombes and Shapiro, 1985;Van Dorsten et al, 1997;Ellington and Kinsey, 1998).…”

“…Stephen T. Kinsey (Mainwood and Rakusan, 1982;Meyer et al, 1984;Hubley et al, 1997;Aliev and Saks, 1997;Kemp et al, 1998;Vendelin et al, 2000;Saks et al, 2003). The intracellular diffusive flux of high-energy phosphates is largely mediated by phosphagen kinases, such as creatine kinase (CK) and arginine kinase (AK), although the mechanistic details are still the subject of study (reviewed by Walliman et al, 1992;Ellington, 2001).…”