ISSN:
1432-2013
Keywords:
Patch clamp
;
Verapamil
;
Charyb-dotoxin
;
Apamin
;
K+ channel blocker
;
Permselectivity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The luminal membrane of principal cells of rat cortical collecting duct (CCD) is dominated by a K+ conductance. Two different K+ channels are described for this membrane. K+ secretion probably occurs via a small-conductance Ca2+-independent channel. The function of the second, large-conductance Ca2+-dependent channel is unclear. This study examines properties of this channel to allow a comparison of this K+ channel with the macroscopic K+ conductance of the CCD and with similar K+ channels from other preparations. The channel is poorly active on the cell. It has a conductance of 263±11 pS (n=36, symmetrical K+ concentrations) and of 139±3 pS (n=91) with 145 mmol/l K+ on one side and 3.6 mmol/l K+ on the other side of the membrane. Its open probability is high after excision (0.71±0.03, n=85). The channel flickers rapidly between open and closed states. Its permeability in the cell-free configuration was 7.0±0.2×10−13 cm3/s (n=85). It is inhibited by several typical blockers of K+ channels such as Ba2+, tetraethylammonium, quinine, and quinidine and high concentrations of Mg2+. The Ca2+ antagonists verapamil and diltiazem also inhibit this K+ channel. As is typical for the maxi K+ channel, it is inhibited by charybdotoxin but not by apamin. The selectivity of this large-conductance K+ channel demonstrates significant differences between the permeability sequence (P K 〉 P Rb 〉 P NH4 〉 P Cs=P Li=P Na=P choline=0) and the conductance sequence (g K 〉 g NH4 〉 g Rb 〉 g Li=g choline 〉 g Cs=g Na=0). The only other cations that are significantly conducted by this channel besides K+ (g K at V c =∞ is 279±8 pS, n=88) are NH 4 + (g NH4=127±22 pS, n=10) and Rb+ (g Rb=36±5 pS, n=6). The K+ currents through this channel are reduced by high concentrations of choline+, Cs+, Rb+, and NH 4 + . These properties and the dependence of this channel on Ca2+ and voltage classify it as a “maxi” K+ channel. A possible physiological function of this channel is discussed in the accompanying paper.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00375076
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