ISSN:
1432-1424
Keywords:
Paramecium
;
patch clamp
;
K channels
;
Ca i 2+ -dependence
;
hyperpolarization activated
;
run-down
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary We have studied a class of Ca i 2+ -dependent K channels in inside-out excised membrane patches fromParamecium under patch clamp. Single channels had a conductance of 72 ±9.0 pS in a solution containing 100mM 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∶〈0.1. The channel activity was dependent on Ca i 2+ , which was applied to the cytoplasmic side; the Ca i 2+ concentration for the half maximal activation was 2 μm. The Hill coefficient for the Ca i 2+ dependence of the channel activity was 2.58, indicating that more than two Ca i 2+ bindings are necessary for full activation. Unlike most Ca i 2+ -dependent K channels in other organisms, the channels inParamecium were slightly more active upon hyperpolarization than upon depolarization. The voltage dependence was fitted to a Boltzmann curve with 41.2 mV pere-fold change in channel activity. While a high Ca i 2+ concentration activated the channels, it also irreversibly reduced the channel activity over time. The decay of channel activity occurred faster at higher Ca i 2+ concentrations. Quaternary ammonium ions suppressed ion passage through the channel; more highly alkylated quaternary ammonium ions were more efficient in blocking. Ba i 2+ and Ca i 2+ were relatively ineffective in blockage. It was concluded that these Ca i 2+ -dependent K channels inParamecium are different from the previously described Ca i 2+ -dependent K channels, and are perhaps of a novel class.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01871166
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