Biophysical and pharmacological characteristics of native two-pore domain TASK channels in rat adrenal glomerulosa cells.
Multiple genes of the TASK subfamily of two-pore domain K(+) channels are reported to be expressed in rat glomerulosa cells. To determine which TASK isoforms contribute to native leak channels controlling resting membrane potential, patch-clamp studies were performed to identify biophysical and pharmacological characteristics of macroscopic and unitary K(+) currents diagnostic of recombinant TASK channel isoforms. Results indicate K(+) conductance (gK(+)) is mediated almost exclusively by a weakly voltage-dependent (leak) K(+) channel closely resembling TASK-3. Leak channels exhibited a unitary conductance approximating that expected for TASK-3 under the recording conditions employed, brief mean open times and a voltage-dependent open probability. Extracellular H(+) induced voltage-independent inhibition of gK(+), exhibiting an IC(50) of 56 nM: (pH 7.25) and a Hill coefficient of 0.75. Protons inhibited leak channel open probability (P(o)) by promoting a long-lived closed state (tau > 500 ms). Extracellular Zn(2+) mimicked the effects of H(+); inhibition of gK(+) exhibited an IC(50) of 41 microM: with a Hill coefficient of 1.26, inhibiting channel gating by promoting a long-lived closed state. Ruthenium red (5 microM: ) inhibited gK(+) by 75.6% at 0 mV. Extracellular Mg(2+) induced voltage-dependent block of gK(+), inhibiting unitary current amplitude without affecting mean open time. Bupivacaine induced voltage-dependent block of gK(+), exhibiting IC(50) values of 116 microM: at -100 mV and 28 microM: at 40 mV with Hill coefficients of 1 at both potentials. Halothane induced a voltage-independent stimulation of gK(+) primarily by decreasing the leak channel closed-state dwell time.
Lotshaw
David P
DP
Department of Biological Sciences, Northern Illinois University, DeKalb, 60115, USA. dlotshaw@niu.edu
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology; D002412:Cations / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D024683:Potassium Channels, Tandem Pore Domain / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D015384:Zona Glomerulosa / Q000166:cytology / Q000502:physiology*
D000779:Anesthetics, Local; D002412:Cations; C407082:Kcnk9 protein, rat; D024683:Potassium Channels, Tandem Pore Domain; D020033:Protein Isoforms; D011994:Recombinant Proteins; D002045:Bupivacaine