The ionic selectivity of the Ca(2+)-activated K(+) channel of Aplysia neurons and of the light-dependent K(+) channel of Pecten photoreceptors to metal and organic cations was studied. The selectivity sequence determined from reversal potential measurements is T1(+) K(+) > Rb(+) > NH(+) (4) > Cs(+) > Na(+), Li(+) and is identical to the sequence determined previously for voltage-dependent K(+) channels in a variety of tissues. Our results suggest that some physical aspect of the K(+) channel is conserved in phyllogenetically different tissues and cells.
The role of the nucleus in the generation of the circadian rhythm in Acetabularia has been nuclear. Early experiments showed that the plant could exhibit a circadian rhythm in the absence of a nucleus. However, other experiments appeared to show that the nucleus could impart phase information to the rhythm, and so therefore must be a part of the system that generates the rhythm. We have conducted experiments similar to these--in particular, one in which the nuclear end of the plant was entrained on a light-dark cycle that was opposite that of the rest of the plant. The phase of the free-running rhythm of this type of plant is not consistent with the conclusion that the nucleus is part of the circadian oscillator. We have also tried entraining opposite ends of plants with no nuclei on opposite light-dark cycles. The ultimate phases of these plants appear to be nearly random. A possible interpretation of these experiments is discussed.
We investigated the dependence of the kinetics of the Ca2+-activated K+ current of the molluscan neuron soma upon membrane potential. The K+ current was activated by intracellular Ca2+ ion injection in neurons with blocked inward Na+ and Ca2+ currents. The difference between currents was measured with brief pulses (less than 100 ms) before and immediately after Ca2+ injection and was used as the Ca2+ activated K+ current at difference membrane potentials. The results in normal (10 mM) and in high (200 nM) external K+ show that the time-course of the Ca2+-activated K+ current depends upon membrane voltage and that the current activates more rapidly with membrane depolarization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.