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Groupe de Recherche en Transport Membranaire, Université de Montréal, Montreal, Quebec, Canada H3C 3J7
The cell-attached configuration of the patch-clamp technique was
used to investigate the effects of taurine on the basolateral potassium
channels of rabbit proximal convoluted tubule. In the absence of
taurine, the previously reported ATP-blockable channel, KATP, was observed in 51% of
patches. It is characterized by an inwardly rectifying current-voltage
curve with an inward slope conductance of 49 ± 5 pS
(n = 15) and an outward slope
conductance of 13 ± 6 pS (n = 15).
The KATP channel open probability
(Po) is low,
0.15 ± 0.06 (n = 15) at a
Vp = 100 mV (Vp
is the pipette potential), and increases slightly with depolarization.
The gating kinetics are characterized by one open time constant
(
o = 5.0 ± 1.9 ms,
n = 6) and two closed time constants
(C1 = 5.2 ± 1.5 ms,
C2 = 140 ± 40 ms;
n = 6). In 34% of patches, a second
type of potassium channel, sK, with distinct properties was recorded. Its current-voltage curve is characterized by a sigmoidal shape, with
an inward slope conductance of 12 ± 2 pS
(n = 4). Its
Po is voltage
independent and averages 0.67 ± 0.03 (n = 4) at
Vp = 80 mV. Both its open time and closed time distributions are described by a single time constant
(o = 96 ± 19 ms,
C = 10.5 ± 3.6 ms;
n = 4). Extracellular perfusion of 40 mM taurine fails to affect sK channels, whereas
KATP channel
Po decreases by
75% (from 0.17 ± 0.06 to 0.04 ± 0.02, n = 7, P < 0.05). In conclusion, the
absolute basolateral potassium conductance of rabbit proximal tubules
is the resulting combination of, at least, two types of potassium
channels of roughly equal importance: a high-conductance low-open
probability KATP channel and a
low-conductance high-open probability sK channel. The previously
described decrease in the basolateral absolute potassium conductance by
taurine is, however, mediated by a single type of K channel: the
ATP-blockable K channel.
patch clamp; regulatory volume decrease; potassium conductance; adenosine 5'-triphosphate-dependent potassium channel; low-conductance potassium channel
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