Spatial non-uniformity of excitation-contraction coupling can enhance arrhythmogenic-delayed afterdepolarizations in rat cardiac muscle.
OBJECTIVE
We examined whether non-uniform muscle contraction affects delayed afterdepolarizations (DADs) by dissociating Ca(2+) from myofilaments within the border zone (BZ) between contracting and stretched regions.


RESULTS
Force, sarcomere length (SL), membrane potential, and [Ca(2+)](i) dynamics were measured in 31 ventricular trabeculae from rat hearts. Non-uniform muscle contraction was produced by exposing a restricted region of muscle to a jet of solution containing 20 mmol/L 2,3-butanedione monoxime (BDM). DADs were induced by 7.5 s-2 Hz stimulus trains at an SL of 2.0 microm (24 degrees C, [Ca(2+)](o) 2.0 mmol/L). The BDM jet enhanced DADs (n = 6, P < 0.05) and aftercontractions (n = 6, P < 0.05) with or without 100 micromol/L streptomycin and occasionally elicited an action potential. A stretch pulse from an SL of 2.0 microm to 2.1 or 2.2 microm during the last stimulated twitch of the trains accelerated Ca(2+) waves in proportion to the increment of force by the stretch (P < 0.01) with or without streptomycin. In the presence of 1 mmol/L caffeine, rapid shortening of the muscle after the stretch pulse increased [Ca(2+)](i) within the BZ, whose amplitude correlated with the increment of force by the stretch (n = 15, P < 0.01).


CONCLUSIONS
These results suggest that non-uniform muscle contraction can enhance DADs by dissociating Ca(2+) from myofilaments within the BZ and thereby cause triggered arrhythmias.
Miura
Masahito
M
Department of Clinical Physiology, Health Science, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574, Japan. mmiura@cardio.med.tohoku.ac.jp
Wakayama
Yuji
Y
Endoh
Hideaki
H
Nakano
Makoto
M
Sugai
Yoshinao
Y
Hirose
Masanori
M
Ter Keurs
Henk E D J
HE
Shimokawa
Hiroaki
H
D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D051381:Rats
D002121:Calcium Channel Blockers; C004717:diacetylmonoxime; D003931:Diacetyl; D002118:Calcium