Abstract
Voltage clamp analysis of the transient outward (positive dynamic) current was performed in sheep Purkinje fibers at a pulse frequency of 1/min. 4-aminopyridine (4-AP, 1 mM) suppressed most of the transient outward current, thus revealing the slow inward current,i si, and an associated brief outward current,i bo. The long lasting component of the current suppressed by 4-AP was labelledi lo. In the presence of 4-AP,i bo was suppressed either by caffeine 10 mM or when Sr was substituted for Ca, both conditions makingi si clearly detectable. Mn ions suppressed bothi si andi bo. Current decay was a monoexponential process fori bo (τ=12 ms) and a two exponential process fori lo (τ1=80−100 ms, τ2=250−400 ms). The peak amplitude-E m relationships were different for the two currents. It was shown that the reversal potential ofi lo was not measureble by the usual method probably because of the too fast activation-deactivation kinetics of the current.
It is concluded that not one but two transient outward currents with different electrophysiological and pharmacological characteristics exist in the sheep Purkinje fiber. The reason of the caffeine-sensitivity ofi bo is discussed.
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Coraboeuf, E., Carmeliet, E. & Prenen, J. Existence of two transient outward currents in sheep cardiac Purkinje fibers. Pflugers Arch. 392, 352–359 (1982). https://doi.org/10.1007/BF00581631
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DOI: https://doi.org/10.1007/BF00581631