Unitary conductance variation in Kir2.1 and in cardiac inward rectifier potassium channels
Por:
Picones A., Keung E., Timpe L.C.
Publicada:
1 ene 2001
Resumen:
Kir2.1 (IRK1) is the complementary DNA for a component of a cardiac inwardly rectifying potassium channel. When Kir2.1 is expressed in Xenopus oocytes or human embryonic kidney (HEK) cells (150 mM external KCI), the unitary conductances form a broad distribution, ranging from 2 to 33 pS. Channels with a similarly broad distribution of unitary conductance amplitudes are also observed in recordings from adult mouse cardiac myocytes under similar experimental conditions. In all three cell types channels with conductances smaller, and occasionally larger, than the ?30 pS ones are found in the same patches as the ?30 pS openings, or in patches by themselves. The unitary conductances in patches with a single active channel are stable for the durations of the recordings. Channels of all amplitudes share several biophysical characteristics, including inward rectification, voltage sensitivity of open probability, sensitivity of open probability to external divalent cations, shape of the open channel i-V relation, and Cs+ block. The only biophysical difference found between large and small conductance channels is that the rate constant for Cs+ block is reduced for the small-amplitude channels. The unblocking rate constant is similar for channels of different unitary conductances. Apparently there is significant channel-to-channel variation at a site in the outer pore or in the selectivity filter, leading to variability in the rate at which K+ or Cs+ enters the channel.
Filiaciones:
Picones A.:
Department of Physiology, University of California-San Francisco, San Francisco, CA 94143, United States
Keung E.:
Section of Cardiology, Department of Veterans Affairs Medical Center, San Francisco, CA 94121, United States
Timpe L.C.:
Section of Cardiology, Department of Veterans Affairs Medical Center, San Francisco, CA 94121, United States
1429 Cabrillo Ave., Burlingame, CA 94010, United States
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