hyperpolarise

Hyperpolarise (British spelling) or hyperpolarize refers to an increase in polarization beyond a reference level. In biology, it most commonly means a change in a cell’s membrane potential that makes the inside more negative than its resting potential. In physics and chemistry, hyperpolarisation describes a higher degree of spin or nuclear polarization than at thermal equilibrium.

In neuroscience, hyperpolarization occurs when potassium channels open or when inhibitory receptors increase chloride conductance, driving the membrane potential further from the threshold. It reduces excitability, influences synaptic integration, and underlies the afterhyperpolarization following action potentials.

Hyperpolarisation also occurs in cardiac and smooth muscle tissues as part of normal electrical regulation, contributing to the timing of contractions. The term describes similar shifts toward a more negative membrane potential in various cell types, often mediated by ion channel activity or ion gradients.

In physical chemistry and imaging, hyperpolarisation is exploited to boost signals in nuclear magnetic resonance and magnetic resonance imaging. Techniques include dynamic nuclear polarization (DNP), spin-exchange optical pumping (SEOP), and parahydrogen-induced polarization (PHIP), which transfer spin order from electrons or parahydrogen to nuclei, yielding substantial signal enhancements.