Circulation Research RES Intact Heart Loose Patch Photolysis Reveals Ionic Current Kinetics During Ventricular Action Potentials Ionic Currents in Intact Hearts CIRCRES/2015/307399 CIRCRES/2015/307399 10.1161/CIRCRESAHA.115.307399 118 01/22/16 2 Bridges-Lyman Gemma 410-3275005 410-3279322 Jalife, José University of Michigan Prof. Ariel L Escobar aescobar4@ucmerced.edu Prof. University of California, Merced 5200 N Lake Rd Merced California 95348 UNITED STATES 2092284618 36968 Josefina Ramos-Franco Rush University Medical Center Josefina_Ramos-Franco@rush.edu 295543 Yuriana Aguilar-Sanchez University of California, Merced yaguilar@ucmerced.edu 192421 Ariel L Escobar University of California, Merced aescobar4@ucmerced.edu 36968 08/10/2015 08/10/2015 10/31/2015 11/12/2015 11/12/2015 New Methods excitation-contraction coupling ventricular action potentials <p><i><b><u>Rationale:</u></b></i> 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 (LPP) technique can provide striking new insights into cardiac function at the whole heart level during health and disease. </p><p><i><b><u>Objective:</u></b></i> To measure transmembrane ionic currents during an AP in order to determine how and when surface Ca²⁺ influx that triggers Ca²⁺ induced Ca²⁺ release (CICR) occurs and how Ca²⁺ activated conductances can contribute to the genesis of AP phase 2. </p><p><i><b><u>Methods and Results:</u></b></i> LPP allows the measurement of transmembrane ionic currents in intact hearts. During a triggered AP, a voltage-dependent Ca²⁺ conductance was fractionally activated (dis-inhibited) by rapidly photo-degrading nifedipine, the Ca²⁺ 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 Ca²⁺ through the L-type channel, CaV 1.2. The late component was identified as a Na⁺-Ca²⁺ exchanger (NCX) current mediated by Ca²⁺ released from the sarcoplasmic reticulum (SR). </p><p><i><b><u>Conclusions:</u></b></i> The novel LPP technique allowed the dissection of transmembrane ionic currents in the intact heart. We were able to determine that during an AP L-Type Ca²⁺ current contributes to phase 1 while NCX contributes to phase 2. In addition, LPP revealed that the influx of Ca²⁺ through L-type Ca²⁺ channels terminates due to voltage-dependent deactivation and not by Ca²⁺ dependent inactivation, as commonly believed. </p> 0 0 0 8 8 no yes CircRes_CIRCRES-2015-307399.xml CircRes_CIRCRES-2015-307399_file1.docx CircRes_CIRCRES-2015-307399_supp1.pdf

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CircRes_CIRCRES-2015-307399_supp2.pdf CircRes_CIRCRES-2015-307399_supp3.pdf CircRes_CIRCRES-2015-307399_supp4.pdf CircRes_CIRCRES-2015-307399_supp5.pdf CircRes_CIRCRES-2015-307399_merge.pdf CircRes_CIRCRES-2015-307399_Ramos-Franco_295543_disclosure.pdf CircRes_CIRCRES-2015-307399_Ramos-Franco_295543_copyright.pdf CircRes_CIRCRES-2015-307399_Escobar_36968_disclosure.pdf CircRes_CIRCRES-2015-307399_Escobar_36968_copyright.pdf CircRes_CIRCRES-2015-307399_Aguilar-Sanchez_192421_disclosure.pdf CircRes_CIRCRES-2015-307399_Aguilar-Sanchez_192421_copyright.pdf PAP: 11/12/15 Please note that the authors have agreed to pay $1275 in excess page charges. Funding: Howard Hughes Medical Institute (HHMI): No National Institutes of Health (NIH): Yes Not applicable for this manuscript: No Other: Yes Wellcome Trust: No Subject Codes: [10003] Electrophysiology [10016] Calcium Cycling/Excitation-Contraction Coupling [10032] Ion Channels/Membrane Transport gbridgeslyman