Markov modelling of ensemble current relaxations: bovine adrenal nicotinic receptor currents analysed.

1. A general approach to the analysis of ensemble currents of ligand-gated channels is presented, with a variety of examples that include single and multiple agonist binding steps, desensitization and several blocking pathways. 2. The use of matrix methods to describe model reaction schemes leads to a simplification if the reaction scheme is irreversible: the product of the exponential relaxation rate constants is exactly equal to the product of the forward reaction steps. 3. This method of analysis applied to the bovine adrenal nicotinic receptor suggests that in the range of acetylcholine concentrations from 1 microM to 2 mM, a model with a single kinetically relevant agonist binding step is appropriate. 4. Complex models, to explain the presence of two desensitizing components in currents recorded from whole cells, may be discounted in favour of two distinct receptor types. 5. A simple model of open channel block is discounted, and desensitization of the blocked state proposed.