Cation specificity and pharmacological properties of the Ca(2+)-dependent K+ channel of rat cortical collecting ducts.
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 Ca(2+)-independent channel. The function of the second, large-conductance Ca(2+)-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 x 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+ antagonist 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 (pK > pRb > pNH4 > pCs = pLi = pNa = pcholine = 0) and the conductance sequence (gK > gNH4 > gRb > gLi = gcholine > gCs = gNa = 0). The only other cations that are significantly conducted by this channel besides K+ (gK at Vc = infinity is 279 +/- 8 pS, n = 88) re NH+4 (gNH4 = 127 +/- 22 pS, n = 10) and Rb+ (gRb = 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.
Schlatter
E
E
Albert-Ludwigs-Universität, Physiologisches Institut, Freiburg, Federal Republic of Germany.
Bleich
M
M
Hirsch
J
J
Markstahler
U
U
Fröbe
U
U
Greger
R
R
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology*; D018999:Charybdotoxin; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D010539:Permeability; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012604:Scorpion Venoms / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002412:Cations; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D001030:Apamin; D002118:Calcium