Key result
Replacing potassium with thallium increases inwardly rectifying and reduces diastolic currents in canine Purkinje strands.
Why the study?
The effects of thallium on membrane currents at diastolic potentials in canine cardiac Purkinje strands were investigated to understand its impact on inward rectifier and pace-maker currents.
Thallium has opposite effects on the pace-maker current and the inward rectifier in canine cardiac Purkinje strands, supporting evidence that the pace-maker current is distinct from the background inward rectifier.
Supports distinction of pacemaker from inward rectifier currents in canine Purkinje strands; leaves open relevance to human electrophysiology.
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.
No takes yet. Share an insight, caveat, or question.
Cohen et al. (1986) studied this question. Thallium (Tl+) vs. Potassium (K+) was evaluated on Membrane currents at diastolic potentials. Thallium replacement of potassium increases the instantaneous inwardly rectifying current and reduces or reverses the diastolic time-dependent current in canine cardiac Purkinje strands.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: