title: Toxin pharmacology of the large-conductance Ca(2+)-activated K+ channel in the apical membrane of rabbit proximal convoluted tubule in primary culture.
abstract: The patch-clamp technique was used to study the toxin pharmacology of the large-conductance Ca(2+)-activated K+ channel (BKCa) present in the apical membrane of rabbit proximal convoluted tubules (PCT) in primary culture. Experiments were performed with the inside-out configuration. This channel was very selective for K+ against Na+ and had a conductance of 180 pS with 140 mmol/l in the pipette and the bath. The action of toxins was studied on the extracellular side of the channel by using the pipette perfusion technique. Experimental conditions were 140 mmol/l KCl in the pipette and 140 mmol/l NaCl in the bath. Pipette potential was maintained at 0 mV. Perfusion of crude venom from Leiurus quinquestriatus hebraeus inhibited reversibly the open probability (Po) in a concentration-dependent fashion (IC50 = 0.8 mg/l; n = 3). The following synthetic or purified toxins were tested: synthetic charybdotoxin (ChTX) IC50 = 7.3 x 10(-9) M (n = 5); iberiotoxin (IbTX) IC50 = 5.5 x 10(-7) mol/l (n = 3); and kaliotoxin (KTX) IC50 = 4.8 x 10(-7) mol/l (n = 3). The suppression of the six first N-terminal amino-acids slightly reduced the affinity of ChTX (IC50 = 1.2 x 10(-8) mol/l, n = 4). Neither Dendroaspis polylepis venom nor purified alpha dendrotoxin modified Po even at high concentrations (20 mg/l and 10(-6) mol/l respectively). Apamin, which blocked the small-conductance K+ channel in cultured PCT, did not act on BKCa. These results indicate that ChTX is the most efficient known toxin against the epithelial BKCa in primary cultures of PCT.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Département de Biologie Cellulaire et Moléculaire, CEN Saclay, Gif sur Yvette, France.
authors.forename: M
authors.initials: M
authors.lastname: Tauc
authors.forename: P
authors.initials: P
authors.lastname: Congar
authors.forename: V
authors.initials: V
authors.lastname: Poncet
authors.forename: J
authors.initials: J
authors.lastname: Merot
authors.forename: C
authors.initials: C
authors.lastname: Vita
authors.forename: P
authors.initials: P
authors.lastname: Poujeol
mesh_terms: D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D018999:Charybdotoxin; D004285:Dogs; D004546:Elapid Venoms / Q000494:pharmacology; D004553:Electric Conductivity; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D008297:Male; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012604:Scorpion Venoms / Q000494:pharmacology*; D012910:Snake Venoms / Q000494:pharmacology*
chemical_list: D004546:Elapid Venoms; D010455:Peptides; D015221:Potassium Channels; D012604:Scorpion Venoms; D012910:Snake Venoms; C072276:kaliotoxin; D018999:Charybdotoxin; D001030:Apamin; D011189:Potassium Chloride; C020273:dendrotoxin; C064719:iberiotoxin; D002118:Calcium