title: Intact Heart Loose Patch Photolysis Reveals Ionic Current Kinetics During Ventricular Action Potentials.
abstract: BACKGROUND
  Assessing the underlying ionic currents during a triggered action potential (AP) in intact perfused hearts offers the opportunity to link molecular mechanisms with pathophysiological problems in cardiovascular research. The developed loose patch photolysis technique can provide striking new insights into cardiac function at the whole heart level during health and disease.
  
  
  OBJECTIVE
  To measure transmembrane ionic currents during an AP to determine how and when surface Ca(2+) influx that triggers Ca(2+)-induced Ca(2+) release occurs and how Ca(2+)-activated conductances can contribute to the genesis of AP phase 2.
  
  
  RESULTS
  Loose patch photolysis allows the measurement of transmembrane ionic currents in intact hearts. During a triggered AP, a voltage-dependent Ca(2+) conductance was fractionally activated (dis-inhibited) by rapidly photo-degrading nifedipine, the Ca(2+) channel blocker. The ionic currents during a mouse ventricular AP showed a fast early component and a slower late component. Pharmacological studies established that the molecular basis underlying the early component was driven by an influx of Ca(2+) through the L-type channel, CaV 1.2. The late component was identified as an Na(+)-Ca(2+) exchanger current mediated by Ca(2+) released from the sarcoplasmic reticulum.
  
  
  CONCLUSIONS
  The novel loose patch photolysis technique allowed the dissection of transmembrane ionic currents in the intact heart. We were able to determine that during an AP, L-type Ca(2+) current contributes to phase 1, whereas Na(+)-Ca(2+) exchanger contributes to phase 2. In addition, loose patch photolysis revealed that the influx of Ca(2+) through L-type Ca(2+) channels terminates because of voltage-dependent deactivation and not by Ca(2+)-dependent inactivation, as commonly believed.
authors.affiliation: From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA.
authors.forename: Josefina
authors.initials: J
authors.lastname: Ramos-Franco
authors.affiliation: From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA.
authors.forename: Yuriana
authors.initials: Y
authors.lastname: Aguilar-Sanchez
authors.affiliation: From the Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL (J.R.-F.); and Quantitative Systems Biology Program, School of Natural Sciences (Y.A.-S.) and Biological Engineering and Small Scale Technologies Program, School of Engineering (A.L.E.), University of California, Merced, CA. aescobar4@ucmerced.edu.
authors.forename: Ariel L
authors.initials: AL
authors.lastname: Escobar
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D056966:Excitation Contraction Coupling; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism*; D000067268:Isolated Heart Preparation; D007700:Kinetics; D008297:Male; D008807:Mice, Inbred BALB C; D008856:Microscopy, Fluorescence / Q000379:methods*; D009543:Nifedipine / Q000737:chemistry / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010782:Photolysis; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: C514350:CACNA1C protein, mouse; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D019831:Sodium-Calcium Exchanger; D009543:Nifedipine
keywords: action potentials; calcium signaling; excitation contraction coupling; ionic currents; nifedipine; sarcoplasmic reticulum