Summary
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1.
Voltage clamp hyperpolarization and depolarization elicited current records consistent with depletion and accumulation, respectively, of potassium in the extracellular clefts of cardiac Purkinje fibers. Hyperpolarization was shown to shift the reversal potential for the pacemaker current,i K 2, a measure ofE K , to more negative potentials. Upon depolarization, a slowly increasing outward current was observed. Analysis of the tail currents elicited by hyperpolarization revealed that a time-dependent change ing x could not explain the time-dependent outward current. However, the tail currents were consistent with a shift ofE K to more positive potentials during the depolarization.
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2.
Alteration in potassium driving force over time results in a time-dependenti 1 even though the underlying conductance is time-independent [29]. This timedependent current may contribute to the currents usually identified asi K 2 andi x .
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3.
The potential at whichi K 2 reverses direction is altered by the clamp program used to elicit it and is obscured by the superimposition of a time-dependent current due to depletion.
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4.
Records consistent with the extracellular cleft potassium concentration being less than that of the bulk phase in the quiescent fiber were obtained. However, an unequivocal interpretation of these current records could not be made.
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5.
These results suggest that conclusions based on the assumption that potassium driving force remains constant during a voltage clamp pulse may be in error. Thus, time-dependent currents cannot be assumed to result solely from time-dependent conductance changes.
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Supported by SFB 38, Project G2
This work was done during CMB's tenure as a Predoctoral Trainee of the Department of Pharmacology, Northwestern University, Chicago, Illinois 60611, U.S.A., in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Supported by NIH GMS Training Grant 00162
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Baumgarten, C.M., Isenberg, G. Depletion and accumulation of potassium in the extracellular clefts of cardiac Purkinje fibers during voltage clamp hyperpolarization and depolarization. Pflugers Arch. 368, 19–31 (1977). https://doi.org/10.1007/BF01063450
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DOI: https://doi.org/10.1007/BF01063450