Focal extracellular potential: A means to monitor electrical activity in single cardiac myocytes

Tara L. Riemer, Leslie Tung

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The focal extracellular potential (FEP) described in this study is an electrophysiological signal related to the transmembrane potential (V(m)) of cardiac myocytes that avoids the mechanical fragility, interference with contraction, and intracellular contact associated with conventional whole cell recording. One end of a frog ventricular myocyte was secured into a glass holding pipette. The FEP was measured differentially between this pipette and a bath pipette while the cell was voltage- or current-clamped by a third whole cell pipette. The FEP appeared as an amplitude-truncated action potential, while FEP duration accurately reflected the action potential duration (APD) at 90% repolarization (APD90). FEP magnitude increased as the holding pipette K+ concentration ([K+]) was increased. The FEP-voltage relation was quasi-linear at negative V(m) with a slope that increased with elevated holding pipette [K+]. Increasing the membrane conductance inside the holding pipette by adding amphotericin B or cromakalim linearized the FEP-voltage relation across all V(m). The FEP accurately reported electrical activation and APD90 during changes of stimulation frequency and episodes of cellular stretch.

Original languageEnglish (US)
Pages (from-to)H1383-H1394
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number4 47-4
StatePublished - Apr 2000


  • Action potential duration
  • Cardiac electrophysiology
  • Frog
  • Voltage clamp

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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