PROPERTIES OF SINGLE-ION CHANNEL CURRENTS ELICITED BY A PULSE OF AGONIST CONCENTRATION OR VOLTAGE

Experiments are often performed to study the behaviour of a single ion channel in response to a perturbation produced by a step change ('jum p') in a variable that influences its equilibrium position, for exampl e a voltage jump or jump in agonist concentration. It is also common t o apply a rectangular pulse (consisting of an on jump followed by an o ff jump); for example brief concentration pulses are used to mimic syn aptic transmission. Assuming a general Markov mechanism for channel dy namics, we obtain theoretical probability distributions of observable characteristics that describe the nonstationary behaviour of single io n channels which are subject to a jump, or to a pulse of finite durati on. These characteristics are such things as open times, shut times, f irst latency, burst length and length of activation. We concentrate pa rticularly on jumps to or from a zero level of agonist, which necessit ates some modification to the usual arguments to cope with having some absorbing sets of states. Where possible, we include results which ma ke allowance for the phenomenon of time interval omission, whereby som e short intervals may be missed due to imperfect resolution of the rec ording method. A numerical example is studied in detail.