Relationship between sarcoplasmic reticular calcium release and Na+-Ca2+ exchange in the rat myocardial contraction.
- Author:
Eun Gi KIM
1
;
Soon Jin KIM
;
Chang Mann KO
Author Information
1. Department of Pharmacology, Yonsei University Wonju-College of Medicine, Wonju, Korea.
- Publication Type:Original Article
- MeSH:
Action Potentials;
Adult;
Animals;
Caffeine;
Calcium*;
Egtazic Acid;
Heart;
Humans;
Muscle Cells;
Myocardial Contraction*;
Nifedipine;
Rats*;
Sarcoplasmic Reticulum
- From:The Korean Journal of Physiology and Pharmacology
2000;4(3):197-210
- CountryRepublic of Korea
- Language:English
-
Abstract:
Suppressive role of Na+-Ca2+ exchange in myocardial tension generation was examined in the negative frequency-force relationship (FFR) of electric field stimulated left atria (LA) from postnatal developing rat heart and in the whole-cell clamped adult rat ventricular myocytes with high concentration of intracellular Ca2+ buffer (14 mM EGTA). LA twitch amplitudes, which were suppressed by cyclopiazonic acid in a postnatal age-dependent manner, elicited frequency-dependent and postnatal age-dependent enhancements after Na+-reduced, Ca2+-depleted (26 Na-0 Ca) buffer application. These enhancements were blocked by caffeine pretreatment with postnatal age-dependent intensities. In the isolated rat ventricular myocytes, stimulation with the voltage protocol roughly mimicked action potential generated a large inward current which was partially blocked by nifedipine or Na+ current inhibition. 0 Ca application suppressed the inward current by 39 +/- 4% while the current was further suppressed after 0 Na-0 Ca application by 53 +/- 3%. Caffeine increased this inward current by 44 +/- 3% in spite of 14 mM EGTA. Finally, the Na+ current-dependent fraction of the inward current was increased in a stimulation frequency-dependent manner. From these results, it is concluded that the Ca2+ exit-mode (forward-mode) Na+-Ca2+ exchange suppresses the LA tension by extruding Ca2+ out of the cell right after its release from sarcoplasmic reticulum (SR) in a frequency-dependent manner during contraction, resulting in the negative frequency-force relationship in the rat LA.
