Ca2+-activated K+ channel in rat pancreatic islet B cells: permeation, gating and blockade by cations.
Activation of Ca2+-dependent K+ conductance has long been postulated to contribute to the cyclical pauses in glucose-induced electrical activity of pancreatic islet B cells. Here we have examined the gating, permeation and blockade by cations of a large-conductance, Ca2+-activated K+ channel in these cells. This channel shares many features with BK (or maxi-K+) Ca2+-activated K+ channels in other cells. (1) Its 'permeability' selectivity sequence is PT1+: PK+: PRb+: PNH4+: PNa+, Li+, Cs+ = 1.3:1.0:0.5:0.17: less than 0.05. Permeant, as well as impermeant, cations reduce channel conductance. (2) Its conductance saturates at 325-350 pS with bath KCl greater than 400 mM (144 mM KCl pipette). (3) It shows asymmetric blockade by tetraethylammonium ion (TEA) and Na+. (4) It is sensitive to Ca2+i over the range 5 nM-100 microM; over the range 50-200 nM, channel activity varies as [Ca2+ free]1-2. (5) It is sensitive to internal pH over the range 6.85-7.35, but the decrease in channel activity seen with reduced pHi may be partially compensated by the increase in free Ca2+ concentration which occurs on acidification of buffered Ca2+/EGTA solutions.
Tabcharani
J A
JA
Department of Medicine (Jewish Hospital), Washington University, St. Louis, MO 63110.
Misler
S
S
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013816:Thermodynamics
D002412:Cations; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium