Related Experiment Videos
Cytoplasmic cellular structures control permeability of outer mitochondrial membrane for ADP and oxidative
E M Fontaine1, C Keriel, S Lantuejoul
1Laboratoire de Bioénergétique, Université Joseph Fourier, Grenoble, France.
Abstract:
The kinetics of regulation mitochondrial respiration by external ADP in permeabilized hepatocytes was studied further. In digitonin-permeabilized hepatocytes, the apparent Km for ADP in regulation of respiration was decreased from 275 +/- 35 microM in control to 48 +/- 8 microM by a treatment with trypsin (15 min, 0.125 mg/ml). In liver tissue homogenates, trypsin treatment similarly decreased the Km value for ADP. These results show that ADP diffusion in hepatocytes may be retarded due to some unknown cytoplasmic trypsin-sensitive protein factor(s) which may be lost during isolation of mitochondria. Since we have previously reported a limited permeability of the outer mitochondrial membrane in isolated hepatocytes (Saks et al. 1995, Biochem. Biophys. Res. Commun., 208, 919-926), we conclude that an important site of control of respiration in liver cells in vivo is located at the porin channels of the outer mitochondrial membrane.
Insights
Mitochondrial respiration regulation by external ADP is controlled by trypsin-sensitive factors in hepatocytes. Trypsin treatment enhances ADP diffusion, suggesting outer mitochondrial membrane porins are key control sites.
Area of Science:
- Biochemistry
- Cellular Respiration
- Mitochondrial Biology
Background:
- Mitochondrial respiration is crucial for cellular energy production.
- Regulation of respiration by external ADP is complex and not fully understood.
- Previous work indicated limited outer mitochondrial membrane permeability in isolated hepatocytes.
Purpose of the Study:
- To investigate the kinetics of mitochondrial respiration regulation by external ADP in permeabilized hepatocytes.
- To identify factors affecting ADP diffusion and its impact on respiration control.
- To determine the specific site of ADP regulation in liver cells in vivo.
Main Methods:
- Studied respiration kinetics in digitonin-permeabilized hepatocytes.
- Applied trypsin treatment to permeabilized hepatocytes and liver homogenates.
- Measured the apparent Km for ADP in regulating respiration.
Main Results:
- Trypsin treatment significantly decreased the apparent Km for ADP in permeabilized hepatocytes (from 275 +/- 35 microM to 48 +/- 8 microM).
- Similar decreases in Km for ADP were observed in liver tissue homogenates after trypsin treatment.
- These findings suggest a cytoplasmic trypsin-sensitive factor(s) retards ADP diffusion.
Conclusions:
- Cytoplasmic factors sensitive to trypsin likely impede ADP diffusion to mitochondria.
- The outer mitochondrial membrane, specifically porin channels, acts as a critical control site for respiration in liver cells in vivo.
- Understanding these regulatory mechanisms is vital for comprehending cellular energy metabolism.