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Effects of thallium on membrane currents at diastolic potentials in canine cardiac Purkinje strands.
Author(s) -
Cohen I S,
Mulrine N K
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp015935
Subject(s) - diastole , chemistry , current (fluid) , purkinje fibers , medicine , electrophysiology , physics , thermodynamics , blood pressure
A two‐micro‐electrode voltage‐clamp technique was used to record membrane currents from canine cardiac Purkinje strands during hyperpolarizing steps to potentials between ‐70 and ‐150 mV in Tyrode solutions containing K+ and/or Tl+. Complete replacement of external K+ by equimolar Tl+ increases the instantaneous inwardly rectifying current. The inwardly rectifying region of the instantaneous I‐V relation is shifted to more positive potentials and its slope is increased. The diastolic time‐dependent current is reduced or reversed. Partial substitution of equimolar Tl+ for K+ reduces the diastolic time‐dependent current. The instantaneous I‐V relation is shifted inward for molar fractions of Tl+ (YTl) greater than 0.5, and is slightly more inward or unchanged for YTl less than or equal to 0.5. Addition of small amounts of Tl+ shifts the instantaneous I‐V relation inward and reduces the diastolic time‐dependent current. Addition of Tl+ in solutions containing Ba2+ to block the background inward rectifier has no effect on the instantaneous I‐V relation; the diastolic time‐dependent (pace‐maker) current is reduced. Block of the pace‐maker current by Tl+ is largely independent of potential in Ba2+ Tyrode solution. Since Tl+ has opposite effects on the pace‐maker current and the inward rectifier, these findings support other evidence that the pace‐maker current is not part of the background inward rectifier.