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.
Lippiat
J D
JD
Ion Channel Group, Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK.
Standen
N B
NB
Davies
N W
NW
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