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Correlation of mitochondrial form and function in vivo: microinjection of substrate and nucleotides
Abstract:
Microinjection of adenine nucleotides and substrates into the cytoplasm of Amoeba proteus followed by EM examination has been used in an attempt to relate alterations in mitochondrial morphology with functional changes. Contracted mitochondria with dark matrix and wide cristae (Type I), and expanded mitochondria with light matrix and narrower cristae (Type II) coexist in normal active amoebae, but their numbers can be varied according to different cell activity states. Following injection of ATP, the mitochondria of the amoebae showed a time-dependent movement towards a predominately Type II form, whilst injections of ADP produced predominately the Type I form. Injection of succinate or deionised water, even in large amounts, had little effect on the numbers of Type I and Type II forms. The change induced by ATP was of long duration; that induced by ADP was influenced by both concentration injected and the cell's substrate levels. With 3 mM solutions of ADP the mitochondrial population was primarily of Type I organelles; higher ADP concentrations or the simultaneous injection of succinate, however, resulted in a switch with time to increased proportions of Type II mitochondria. The results extend the findings of previous in vivo and in vitro mitochondrial studies and are discussed in the light of these.
Insights
Adenine nucleotides like ATP and ADP influence mitochondrial shape in Amoeba proteus. ATP promotes expanded mitochondria (Type II), while ADP favors contracted forms (Type I), affecting cellular energy states.
Area of Science:
- Cell Biology
- Biochemistry
- Microscopy
Background:
- Mitochondria exhibit dynamic morphological changes linked to cellular function.
- Two distinct mitochondrial forms (Type I and Type II) exist in Amoeba proteus, varying with cell activity.
Purpose of the Study:
- To investigate the relationship between adenine nucleotide levels and mitochondrial morphology in Amoeba proteus.
- To elucidate how adenosine triphosphate (ATP) and adenosine diphosphate (ADP) affect mitochondrial structure and potentially function.
Main Methods:
- Microinjection of adenine nucleotides (ATP, ADP) and substrates (succinate) into Amoeba proteus cytoplasm.
- Electron microscopy (EM) examination to analyze mitochondrial morphology (Type I and Type II forms).
Main Results:
- ATP injection induced a time-dependent shift towards Type II (expanded) mitochondria.
- ADP injection predominantly resulted in Type I (contracted) mitochondria.
- Succinate or deionized water injections had minimal impact on mitochondrial morphology; however, high ADP concentrations or co-injection with succinate could lead to a shift towards Type II mitochondria.
Conclusions:
- Adenine nucleotides directly modulate mitochondrial morphology in Amoeba proteus.
- Mitochondrial shape changes induced by ATP and ADP suggest alterations in cellular energy metabolism.
- Findings correlate with existing in vivo and in vitro mitochondrial research, providing insights into dynamic mitochondrial regulation.