Properties of the single Cl channels were studied in excised patches of surface membrane from molluscan neurones using single-channel recording technique. These channels are controlled by Ca2+ and K+ acting on cytoplasmic and outer membrane surfaces, respectively, and by the membrane potential. The channels display about 16 intermediate conductance sublevels, each of them being multiples of approximately 12.5 pS. The upper level of the channel conductance is about 200 pS. The channel behavior is consistent with an aggregation of channel-forming subunits into a cluster.

Earlier we have shown that millimetre microwaves (42.25 GHz) of non-thermal power, upon direct admittance into an experiment bath, greatly influence activation characteristics of single Ca2+-dependent K + channels (in particular, the channel open state probability, Po). Here we present new data showing that similar changes in Po arise due to the substitution of a control bath solution for a preliminary microwave irradiated one of the same composition (100 mmol/l KCI with Ca 2+ added), with irradiation time being 20-30 min. Therefore, due to the exposure to the field the solution acquires some new properties that are important for the channel activity. The irradiation terminated, the solution retains a new state for at least 10-20 rain (solution memory). The data suggest that the effects of the field on the channels are mediated, at least partially, by changes in the solution properties.

Using the patch voltage-clamp method, possible effects of millimetre microwaves (42.25 GHz) on single CaZ+-activated K + channels in cultured kidney cells (Vero) were investigated. It was found that exposure to the field of non-thermal power (about 100 btW/cm 2) for 20-30 min greatly modifies both the Hill coefficient and an apparent affinity of the channels for Ca2~. The data suggest that the field alters both cooperativity and binding characteristics of the channel activation by internal Ca 2+. The effects depend on initial sensitivity of the channels to Ca 2+ and the Ca 2+ concentration applied.

1. Acetylcholine (ACh)-induced currents were studied in completely isolated Lymnaea stagnalis neurones using the voltage-clamp technique. 2. The ACh-activated pathways were shown to be selective for Cl- ions. 3. It was shown that membrane depolarization inhibits ACh-induced conductance. This phenomenon was called 'ACh response inactivation'. 4. Inactivation decreases after lowering the extracellular Ca2+ concentration or after blockade by Mn2+ of the electrically excitable Ca2+ channels. 5. In dialysed neurones an increase of the intracellular Ca2+ concentration inhibits the ACh-induced conductance. 6. The conclusion is made that the inactivation of ACh response by depolarization is initiated by Ca2+ entering the neurone through the electrically excitable Ca channels. 7. The onset and the decay of the ACh response inactivation were studied by analysing the relaxations of the ACh-induced current during and after the application of depolarizing pulses. The most conspicuous relaxation is a slow relaxation observed at the end of a long depolarizing pulse, which appears to reflect the return of the system from the inactivated state to the non-inactivated one. 8. The slow relaxations observed during and after a depolarizing pulse appear correlated with variations of the intracellular Ca2+ concentration, and are distinct from faster relaxations observed in the hyperpolarizing range and attributed to the voltage dependence of the channel open-time.

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