Application of blebbistatin as an excitation-contraction uncoupler for electrophysiologic study of rat and rabbit hearts.
BACKGROUND
Application of fluorescence imaging of cardiac electrical activity is limited by motion artifacts and/or side effects of currently available pharmacologic excitation-contraction uncoupling agents.


OBJECTIVE
The purpose of this study was to test whether blebbistatin, a recently discovered inhibitor of myosin II isoforms, can be used as an excitation-contraction uncoupler.


METHODS
The specificity and potency of blebbistatin were examined by assaying the effects of blebbistatin on the contraction and basic cardiac electrophysiologic parameters of Langendorff-perfused rabbit hearts, isolated rabbit right ventricle and right atrium, and single rat ventricular myocytes using conventional ECG, surface electrograms, microelectrode recordings, and optical imaging with voltage-sensitive and Ca(2+)-sensitive dyes. Action potential morphology, ECG parameters, cardiac conduction, and refractoriness were determined after perfusion with 0.1-10 microM blebbistatin.


RESULTS
Blebbistatin 5-10 microM completely eliminated contraction in all cardiac preparations but did not have any effect on electrical activity, including ECG parameters, atrial and ventricular effective refractory periods, and atrial and ventricular activation patterns. Blebbistatin 10 microM had no effects on action potential morphology in rabbit cardiac tissue. Blebbistatin inhibited single cellular contraction in a dose-dependent manner with half-maximal inhibitory concentration (IC(50)) = 0.43 microM, without altering the morphologies of intracellular calcium transients. The blebbistatin effect was completely reversible by simultaneous washout and photobleaching by ultraviolet light


CONCLUSIONS
Blebbistatin is a promising novel selective excitation-contraction uncoupler that can be used for optical imaging of cardiac tissues.
Fedorov
Vadim V
VV
Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-4899, USA.
Lozinsky
Ilya T
IT
Sosunov
Eugene A
EA
Anyukhovsky
Evgeniy P
EP
Rosen
Michael R
MR
Balke
C William
CW
Efimov
Igor R
IR
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D006325:Heart Atria / Q000187:drug effects; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008297:Male; D008839:Microelectrodes; D023421:Models, Animal; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology; D024462:Myosin Type II / Q000037:antagonists & inhibitors; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D012107:Research Design; D012849:Sinoatrial Node / Q000187:drug effects / Q000502:physiology; D014475:Uncoupling Agents / Q000494:pharmacology*; D016276:Ventricular Function
D006576:Heterocyclic Compounds, 4 or More Rings; D007527:Isoenzymes; D014475:Uncoupling Agents; C472645:blebbistatin; D024462:Myosin Type II