Effect of extracellular calcium on the contractility of warm-and cold-acclimated crucian carp heart |
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Authors: | M Vornanen |
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Institution: | (1) Department of Biology, University of Joensuu, P.O. Box 111, F-80101 Joensuu, Finland |
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Abstract: | Crucian carp (Carassius carassius L.) were acclimated for at least 4 weeks to 2°C or 22°C, and the consequences of thermal acclimation on force development, time-course of contraction and action potential duration of the ventricular myocardium were studied. In cold-acclimated fish contraction was activated at much lower external Ca] than in warm-acclimated fish: Ca] for half-maximal force was 0.9±0.15 and 3.1±0.92 mmol·l-1 (P<0.05) for cold- and warm-acclimated fish, respectively. Durations of contraction and relaxation were significantly longer in fish acclimated to 2°C than in fish acclimated to 22°C, especially at Ca] below 2 mmol·l-1. In low-Ca solution ventricular action potential was prolonged both in cold- and warm-acclimated fish. In 0.5 mmol·l-1 Ca action potential duration at zero voltage level was longer in cold- than warm-acclimated fish. Although lengthening of action potential was evident in both acclimation groups, a marked prolongation of contraction duration by low-Ca solutions occurred only in cold-acclimated fish. This suggests that a plateau component of contraction is present in cold-acclimated fish but less well developed in warm-acclimated fish hearts. Contractions were strongly inhibited by sarcolemmal Ca-channel blocker, cadmium (100 and 300 mol·l-1), in both warm- and cold-acclimated crucian carp hearts. However, the sarcoplasmic reticulum Ca release channel blocker, ryanodine (10 mol·l-1), had no effect on the force of contraction in either acclimation group. These results suggest that the contraction of crucian carp heart is controlled by sarcolemmal mechanisms without contribution by sarcoplasmic reticulum Ca release. Since the Ca sensitivity of myofilaments was not altered by thermal acclimation, the results indicate that thermal acclimation alters Ca activation of contraction of the crucian carp heart at the level of sarcolemma.Abbreviations
AP
action potential
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EGTA
ethyleneglycol-bis-( -aminoethylether)-N,N,N ,N -tetra-acetic acid
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F
max
maximum force
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F
max
maximum rate of contraction
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F
min
maximum rate of relaxation
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HEPES
N-2-hydroxyethylpiperazine-N -2-ethanesulphonic acid
- pCa
log Ca]
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Pl
action potential plateau
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SL
sarcolemma
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SR
sarcoplasmic reticulum
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TPF
time to peak force
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T1/2R
time to half relaxation from the peak force |
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Keywords: | Thermal acclimation Restitution rate Action potential Excitation-contraction coupling Fish heart |
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