Mitochondrial spare respiratory capacity (SRC)

Mitochondrial spare respiratory capacity (SRC), also known as mitochondrial reserve or bioenergetic reserve capacity, is not a discrete molecule or receptor, but rather a functional parameter that quantifies the difference between basal and maximal mitochondrial respiration in cells[1][4][5]. It reflects the ability of mitochondria to respond to increased energy demands or stress by increasing their rate of oxidative phosphorylation above baseline levels. SRC is measured experimentally by comparing oxygen consumption rates before and after stimulation with an uncoupler such as FCCP, which drives maximal electron transport activity[1][4]. SRC serves as an indicator of cellular metabolic flexibility and resilience. A high SRC suggests that mitochondria can meet sudden increases in ATP demand, while low SRC indicates vulnerability to energetic stress and has been associated with pathological states such as cancer (e.g., acute myeloid leukemia), neurodegeneration, cardiovascular diseases, immune dysfunctions, and aging-related decline[2][4][5]. In immune cells like T lymphocytes, higher SRC correlates with better memory formation and long-term persistence; reduced SRC is linked to impaired function after stem cell transplantation or during exhaustion[5]. Although drugs may indirectly affect SRC by targeting components of the electron transport chain (such as complex I inhibitors like metformin or IACS compounds), SRC itself is not a direct drug target but rather a readout for mitochondrial health or drug efficacy/toxicity on cellular energetics[2][3][6]. Thus it should not be classified among canonical therapeutic targets such as receptors or enzymes. In summary: "Mitochondrial spare respiratory capacity" describes a measurable property reflecting how much extra energy mitochondria can produce under stress—not an individual protein/gene/receptor—and therefore does not fit standard molecular target conventions.

Other names

mitochondrial reserve capacityspare bioenergetic capacityrespiratory reserve capacity