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The internal concentration of K+ in isolated rat liver mitochondria
Abstract:
A simple osmotic method has been developed to determine the internal K+ concentration of mitochondria by determining the concentration of external K+ at constant osmotic pressure at which metabolically inhibited mitochondria neither shrink nor swell. This concentration has been found to correspond to approx. 80-85 mM in freshly isolated mitochondria and considerably lower after additional centrifugation procedures. Since mitochondria are in osmotic equilibrium with the suspending medium (in this case, 0.32 osmolal), and K+ is the primary exchangeable internal ion, a significant proportion of the internal osmotic pressure must be exerted by the sucrose. Results for experiments determining internal K+ after centrifuging mitochondria at various G values confirm the reports of Sitaramam et al. (Sitaraman, V. and Sarma, M.K.J. (1981) Proc. Natl. Acad. Sci. USA 78, 3441-3445 and Sambasivarao, D. and Sitaramam, V. (1983) Biochim. Biophys. Acta 722, 256-270) that centrifugation induces the entry of sucrose in mitochondria isolated in a sucrose medium.
Insights
A new osmotic method accurately measures internal potassium (K+) concentration in mitochondria. Centrifugation significantly reduces this concentration by causing sucrose entry into mitochondria.
Area of Science:
- Biochemistry
- Cell Biology
- Mitochondrial Function
Background:
- Mitochondria play a crucial role in cellular energy production.
- Accurate determination of mitochondrial internal ion concentrations is vital for understanding their function.
- Previous methods for assessing mitochondrial ion concentrations have limitations.
Purpose of the Study:
- To develop a simple osmotic method for determining the internal potassium (K+) concentration of mitochondria.
- To investigate the effect of centrifugation on mitochondrial internal K+ concentration.
Main Methods:
- Developed a simple osmotic method based on monitoring mitochondrial volume changes (swelling or shrinking) at constant osmotic pressure.
- Determined external K+ concentration at which metabolically inhibited mitochondria neither shrink nor swell.
- Measured internal K+ concentration in freshly isolated and centrifuged mitochondria.
Main Results:
- The developed osmotic method allows for the determination of internal K+ concentration in mitochondria.
- Freshly isolated mitochondria exhibit an internal K+ concentration of approximately 80-85 mM.
- Centrifugation procedures lead to a considerable decrease in mitochondrial internal K+ concentration.
- Results indicate that centrifugation induces sucrose entry into mitochondria isolated in a sucrose medium.
Conclusions:
- The developed osmotic method is effective for measuring mitochondrial internal K+ concentration.
- Centrifugation significantly impacts mitochondrial integrity and internal solute composition.
- Sucrose entry during centrifugation affects the measured internal K+ concentration, highlighting the importance of sample preparation methods.