Effects of thallium on membrane currents at diastolic potentials in canine cardiac Purkinje strands.
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.
Cohen
I S
IS
Mulrine
N K
NK
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003971:Diastole; D004285:Dogs; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011690:Purkinje Fibers / Q000502:physiology*; D013793:Thallium / Q000494:pharmacology*; D013997:Time Factors
D007473:Ion Channels; D013793:Thallium; D011188:Potassium