Cell biology and proposed mechanisms
Mitochondrial membrane potential
Mitochondrial membrane potential is the voltage difference across the inner membrane of a mitochondrion, typically around minus 140 to minus 180 millivolts. It is created by pumping protons out and is the stored energy that the ATP-making enzyme then spends. A collapse in it is a standard early sign of cell death.
Also called Δψm, delta psi m, MMP, membrane potential
What it is
As electrons pass along the electron transport chain, three of the four complexes pump protons from the mitochondrial interior into the space between the two mitochondrial membranes. That builds up both a charge difference and a pH difference across the inner membrane. The charge component is the mitochondrial membrane potential, written Δψm. ATP synthase lets the protons back in and uses their flow to make ATP.
Δψm is not a health score. It is a working voltage with a normal operating range. Too low means failing energy production or a cell in the early stages of apoptosis. Sustained excess can increase reactive oxygen species leakage.
How it is measured
Δψm is measured with voltage-sensitive fluorescent dyes such as TMRM or JC-1, in cultured cells or isolated mitochondria under a microscope or flow cytometer.
Where it appears
The photobiomodulation mechanism reviewed in the IEEE Journal of Selected Topics in Quantum Electronics (2016) proposes that red and near-infrared light raises Δψm as an intermediate step towards increased ATP.
Why it matters here
It is a real and precisely defined quantity, and one that can only be measured in a laboratory dish. That is worth knowing when you meet it in an explanation of how red and near infrared light are proposed to work.