Efficiency: an agonist attribute that links binding and gating

Abstract

Agonists are evaluated by a concentration-response curve (CRC), with a midpoint (EC50) that indicates potency and a high-concentration asymptote (Pomax) that indicates efficacy. The low-concentration asymptote indicates constitutive activity and is agonist-independent. A third agonist attribute, efficiency (η eta) is the fraction of binding energy that is applied to the conformational change that activates the receptor. We show that η can be calculated from EC50 and the asymptotes of a CRC for muscle nicotinic acetylcholine receptors (AChR) derived from either single-channel or whole-cell responses.