Plays an important role in maintenance of mitochondrial morphology and in mediating either calcium or potassium/proton antiport (PubMed:18417609, PubMed:32977469, PubMed:35912435, PubMed:36321428). Mediates proton-dependent calcium efflux from mitochondrion (PubMed:35912435, PubMed:36321428). Also functions as an electroneutral mitochondrial proton/potassium exchanger (PubMed:36321428). Required for the mitochondrial tubular network and cristae organization (PubMed:18417609, PubMed:32977469, PubMed:36321428). Involved in apoptotic release of cytochrome c (PubMed:18417609). Inhibits the proteolytic activity of AFG3L2, stimulating respiration and stabilizing respiratory enzymes in actively respiring mitochondria (PubMed:36321428). However, when mitochondria become hyperpolarized, GHITM loses its inhibitory activity toward AFG3L2 and the now the active AFG3L2 turns first on GHITM and, if hyperpolarization persists, on other proteins of the mitochondria, leading to a broad remodeling of the mitochondrial proteome (PubMed:36321428). {ECO:0000269|PubMed:18417609, ECO:0000269|PubMed:35912435, ECO:0000269|PubMed:36321428}. This is the function of GHITM (growth hormone inducible transmembrane protein, Ensembl gene identifier ENSG00000165678).