Calcium-dependent potassium channel in Paramecium studied under patch clamp.
We have studied a class of Ca2+i-dependent K channels in inside-out excised membrane patches from Paramecium under patch clamp. single channels had a conductance of 72 +/- 9.0 pS in a solution containing 100 mM K+. The channels were selective for K+ over Rb+ with the permeability ratio of 1: 0.56, and over Na+, Cs+ or NH+4 with a ratio 1: less than 0.1. The channel activity was dependent on Ca2+i, which was applied to the cytoplasmic side; the Ca2+i concentration for the half maximal activation was 2 microM. The Hill coefficient for the Ca2+i dependence of the channel activity was 2.58, indicating that more than two Ca2+i bindings are necessary for full activation. Unlike most Ca2+i-dependent K channels in other organisms, the channels in Paramecium were slightly more active upon hyperpolarization than upon depolarization. The voltage dependence was fitted to a Boltzmann curve with 41.2 mV per e-fold change in channel activity. While a high Ca2+i concentration activated the channels, it also irreversibly reduced the channel activity over time. The decay of channel activity occurred faster at higher Ca2+i concentrations. Quaternary ammonium ions suppressed ion passage through the channel; more highly alkylated quaternary ammonium ions were more efficient in blocking. Ba2+i and Ca2+i were relatively ineffective in blockage. it was concluded that these Ca2+i-dependent K channels in Paramecium are different from the previously described Ca2+i-dependent K channels, and are perhaps of a novel class.
Saimi
Y
Y
Laboratory of Molecular Biology, University of Wisconsin, Madison 53706.
Martinac
B
B
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D010247:Paramecium / Q000502:physiology*; D010477:Perfusion; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D014743:Videotape Recording
D015221:Potassium Channels; D002118:Calcium