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Am J Physiol Heart Circ Physiol 279: H798-H807, 2000;
0363-6135/00 $5.00
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Vol. 279, Issue 2, H798-H807, August 2000

Altered E-C coupling in rat ventricular myocytes from failing hearts 6 wk after MI

J. Andrew Wasserstrom1,2, Even Holt1, Ivar Sjaastad1, Per Kristian Lunde1, Annlaug Ødegaard1, and Ole M. Sejersted1

1 Institute for Experimental Medical Research, University of Oslo, Ullevaal Hospital, Oslo, Norway; and 2 Departments of Medicine (Cardiology) and Molecular Pharmacology and Biological Chemistry and The Feinberg Cardiovascular Research Institute, Northwestern University Medical School, Chicago, Illinois 60611

Excitation-contraction (E-C) coupling was investigated in rat hearts 6 wk after induction of myocardial infarction (MI) by ligation of the left coronary artery. Heart weight was increased by 74% and left ventricular end-diastolic pressure was 23 ± 2 mmHg in MI compared with 8 ± 2 mmHg in sham-operated controls (Sham, P < 0.001). Cell shortening was measured in voltage-clamped myocytes at 36°C. In solutions where Cs+ had been replaced by K+, the voltage dependence of contraction was sigmoidal between -20 and +100 mV in Sham and MI cells. Verapamil (20 µM) blocked L-type Ca2+ current and reduced contraction in Sham cells by ~50% (P < 0.01) but did not decrease contraction significantly in MI cells at test potentials above +10 mV. Verapamil-insensitive contractions were blocked by Ni2+ (5 mM). Na+/Ca2+ exchange current was doubled in MI compared with Sham cells at test potentials between -20 and +80 mV (P < 0.05), whereas mRNA and protein expression increased by 30-40%. Finally, voltage dependence of contraction was bell shaped in Na+-free solutions, but contraction was significantly increased in MI cells over a wider voltage range (P < 0.05). The insensitivity to Ca2+ channel block in MI cells may result from an increased contribution of the Na+/Ca+ exchanger to triggering of E-C coupling. These results suggest significant changes in E-C coupling in the hypertrophy and failure that develop in response to extensive MI.

calcium channels; contractility; heart failure; hypertrophy; excitation-contraction coupling; myocardial infarction


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