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Fig. 5. Single-channel characteristics of the cloned ccKir2 channels from COS-1
cells and endogenous Kir2 channels of the crucian carp ventricular myocytes.
(A) Comparison of inside-out recordings of the cloned ccKir2 proteins (left)
and cell-attached recordings of the endogenous IK1
currents (right) demonstrating three distinct channel types on the basis of
kinetics and conductance. Horizontal lines indicate the zero current level.
(B) Current–voltage relationships of the ccKir2.1, ccKir2.2 and ccKir2.5
proteins in inside-out recordings from COS-1 cells (left) and cell-attached
recordings of the endogenous IK1 in ventricular myocytes
(right). Endogenous currents are means of all inward-rectifier channel types
present in ventricular myocytes. (C) Conductance variation of endogenous
ccKir2 currents of crucian carp ventricular myocytes in cell-attached (top)
and inside-out (bottom) recordings. Distinct populations of small conductance
(10–14 pS) channels are indicated with arrows. (D) Comparison of open
time distribution (left) and open probability (right) of the cloned ccKir2.5
and ccKir2.2 channels and the endogenous fast and slow IK1
of ventricular myocytes. Open time distributions of the endogenous channels of
temperature-acclimated fish include all recordings of the particular current
type (slow IK1 or fast IK1): good fits
to a monoexponential function suggest the presence of two separate channel
types with different kinetics. Note also the different open time distributions
of the cloned ccKir2.2 and ccKi2.5 channels. (E) Comparison of heterologously
expressed ccKir2.5 and ccKir2.2 channels and endogenous slow and fast
IK1 on the basis of mean open time (
o) and
open probability (Po).
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