Energetics of swelling in isolated hepatocytes: A comprehensive study

Abstract

Cell swelling is now admitted as being a new principle of metabolic control but little is known about the energetics of cell swelling. We have studied the influence of hypo-or hyperosmolarity on both isolated hepatocytes and isolated rat liver mitochondria. Cytosolic hypoosmolarity on isolated hepatocytes induces an increase in matricial volume and does not affect the myxothiazol sensitive respiratory rate while the absolute value of the overall thermodynamic driving force over the electron transport chain increases. This points to an increase in kinetic control upstream the respiratory chain when cytosolic osmolarity is decreased. On isolated rat liver mitochondria incubated in hypoosmotic potassium chloride media, energetic parameters vary as in cells and oxidative phosphorylation efficiency is not affected. Cytosolic hyperosmolarity induced by sodium co-transported amino acids, per se, does not affect either matrix volume or energetic parameters. This is not the case in isolated rat liver mitochondria incubated in sucrose hyperosmotic medium. Indeed, in this medium, adenine nucleotide carrier is inhibited as the external osmolarity increases, which lowers the state 3 respiration close to state 4 level and consequently leads to a decrease in oxidative phosphorylation efficiency. When isolated rat liver mitochondria are incubated in KCI hyperosmotic medium, state 3 respiratory rate, matrix volume and membrane electrical potential vary as a function oftime. Indeed, matrix volume is recovered in hyperosmotic KCI medium and this recovery is dependent on Pi-Kentry. State 3 respiratory rate increases and membrane electrical potential difference decreases during the first minutes of mitochondrial incubation until the attainment of the same value as in isoosmotic medium. This shows that matrix volume, flux and force are regulated as a function of time in KCI hyperosmotic medium. Under steady state, neither matrix volume nor energetic parameters are affected. Moreover, NaCI hyperosmotic medium allows matrix volume recovery but induces a decrease in state 3 respiratory flux. This indicates that potassium is necessary for both matrix volume and flux recovery in isolated mitochondria. We conclude that hypoosmotic medium induces an increase in kinetic control both upstream and on the respiratory chain and changes the oxidative phosphorylation response to forces. At steady state, hyperosmolarity, per se, has no effect on oxidative phosphorylation in either isolated hepatocytes or isolated mitochondria incubated in KCI medium. Therefore, potassium plays a key role in matrix volume, flux and force regulation. (Mol Cell Biochem 184: 107~121, 1998)

Heterogeneity of ADP Diffusion and Regulation of Respiration in Cardiac Cells

“…Fig. 3, left, shows that the high apparent K m for exogenous ADP in permeabilized cardiac fibers was not changed by increasing osmolarity of the solution from isoosmotic (0.24 osM) up to highly hyperosmotic conditions (1.3 osM) by addition of sucrose, which induces significant contraction of sucrose impermeable matrix space and an increase in intermembrane space volume (Devin et al, 1998;Saad-Nehme et al, 2001). The only result is a decrease of V max of respiration, but there are no changes in the apparent K m for ADP ( Fig.…”

Ionic imbalance, in addition to molecular crowding, abates cytoskeletal dynamics and vesicle motility during hypertonic stress

“…High levels of intracellular salt also could affect membrane trafficking by modulating available energy. Increased ion concentration decreases mitochondrial matrix volume and disrupts key parameters of the respiratory chain, as shown in isolated mitochondria (27,28) and as predicted by mathematical models of mitochondrial bioenergetics (29). Thus, hypertonicity conceivably could affect membrane trafficking by decreasing ATP production by mitochondria.…”

Influence of diurnal hyperosmotic loading on the metabolism and matrix gene expression of a whole‐organ intervertebral disc model

“…The precise cellular pathways by which mechanical load is transduced and how cells respond to matrix (ECM) changes in their proximate environment is poorly understood. [23][24][25][26][27][28] Apart from a direct impact on the cytoskeleton, 29 mechanical disc loading causes alterations in matrix osmolarity due to in-and efflux of water. 30,31 In this context, it has been proposed that osmolarity changes within the cell-surrounding matrix are at least partially responsible for maintaining a balanced disc/ECM metabolism.…”