Properties of single ion channel currents elicted by a pulse of agonist concentration or voltage

Abstract

Experiments are often performed to study the behaviour of a single ion channel in response to a perturbation produced by a step change (‘jump’) in a variable that influences its equilibrium position, for example a voltage jump or jump in agonist concentration. It is also common to apply a rectangular pulse (consisting of an on jump followed by an off jump); for example brief concentration pulses are used to mimic synaptic transmission. Assuming a general Markov mechanism for channel dynamics, we obtain theoretical probability distributions of observable characteristics that describe the non–stationary behaviour of single ion channels which are subject to a jump, or to a pulse of finite duration. These characteristics are such things as open times, shut times, first latency, burst length and length of activation. We concentrate particularly on jumps to or from a zero level of agonist, which necessitates some modification to the usual arguments to cope with having some absorbing sets of states. Where possible, we include results which make allowance for the phenomenon of time interval omission, whereby some short intervals may be missed due to imperfect resolution of the recording method. A numerical example is studied in detail.