Block of BK (maxi K) channels of rat pituitary melanotrophs by Na+ and other alkali metal ions.
The block of large-conductance calcium-activated potassium (BK) channels by internal and external alkali metal ions was studied in adult rat melanotrophs. Internal but not external 20 mM Na+ produced a strongly voltage-dependent, flickery block that was well-fitted to the Woodhull model by using a value of 140 mM for the dissociation rate constant at 0 mV [Kd(0)] and an equivalent valence (zdelta) of 0.9. At a concentration of 20 mM external K+, Cs+ and Rb+, but not Li+, caused a rightward shift of the voltage dependence of the intracellular Na+ (Na+i ) block. This effect of K+, Cs+ and Rb+ was modelled by an equilibrium knock-out mechanism in which the block-relieving ion binds to a site located within the voltage field and consequently increases the off-rate of Na+. Internal Li+ caused little or no block whereas internal Cs+ caused a voltage-dependent block [Kd(0) approximately 150 mM]. Flickery channel block observed in cell-attached patches was consistent with a cytoplasmic Na+ activity between 1 and 10 mM.
Kehl
S J
SJ
Department of Physiology, University of British Columbia, Vancouver, B.C., Canada, V6T 1Z3.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002586:Cesium / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008094:Lithium / Q000494:pharmacology; D009074:Melanocyte-Stimulating Hormones / Q000096:biosynthesis*; D008672:Metals, Alkali / Q000494:pharmacology*; D010902:Pituitary Gland / Q000166:cytology* / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects*; D024681:Potassium Channels, Calcium-Activated; D051381:Rats; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*
D051036:Large-Conductance Calcium-Activated Potassium Channels; D008672:Metals, Alkali; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D002586:Cesium; D009074:Melanocyte-Stimulating Hormones; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D011188:Potassium; D002118:Calcium