Correlation of mitochondrial form and function in vivo: microinjection of substrate and nucleotides.

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.