Block of cloned BKCa channels (rSlo) expressed in HEK 293 cells by N-methyl d-glucamine.
We have investigated the conductance properties of large-conductance Ca2+-activated K+ (BKCa) channels formed by stable expression of the rSlo gene in HEK 293 cells. Single-channel recordings were obtained from inside-out patches excised into solution containing 100 microM Ca2+ to ensure a relatively high open probability over the range of membrane potentials studied (-120 to +100 mV). The unitary conductance of these channels at +80 mV was 221.6+/-5.4 pS in symmetrical 140 mM K+. Decreasing the K+ concentration on either side of the membrane, while maintaining ionic strength by adding N-methyl d-glucamine (NMDG+), reduced the unitary conductance. The reduction in conductance was greater when internal K+ was lowered by replacement with NMDG+. However, if sucrose was used as the internal K+ substitute instead of NMDG+ the reduction in unitary conductance was similar to that seen on reducing external K+. A rate-theory model whereby NMDG+ produces a very rapid block of the BKCa channel from the inside, but not the outside, is able to describe our results.
Ion Channel Group, Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK.
J D
JD
Lippiat
N B
NB
Standen
N W
NW
Davies
D000818:Animals; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000166:cytology; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008536:Meglumine / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000096:biosynthesis* / Q000235:genetics; D024681:Potassium Channels, Calcium-Activated; D051381:Rats
D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D008536:Meglumine; D011188:Potassium