We have previously shown that the gating of pairs of sodium channels in neuroblastoma cells is anti-cooperative; i.e., the opening of one channel reduces the probability that the other channel will open. Our analysis indicates that this type of channel anti-cooperatively does not significantly affect the values of parameters, such as channel density or rate of channel opening, that can be obtained from noise spectra. In another type of experiment, we have previously shown that cells of the plant Samanea saman contain potassium channels and that the properties of these channels are consistent with a role in opening of plant leaflets. Experiments performed with varying concentrations of external potassium demonstrated a shift in the threshold for activation. When external potassium was varied from 1 mM to 50 mM, the threshold shifted about 60 mV in the depolarizing direction. The magnitude and direction of the shift are consistent with the view that there is a negative fixed charge on the membrane and that potassium ions can screen this charge.
