Importance of the sarcoplasmic reticulum and adrenergic stimulation on the cardiac contractility of the neotropical teleost Synbranchus marmoratus under different thermal conditions

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 2007-10, Vol.177 (7), p.713-721
• Main Authors: Rocha, Matheus L, Rantin, Francisco T, Kalinin, Ana L
• Format: Article
• Language: English
• Subjects: Acclimatization; Animals; Calcium; Dose-Response Relationship, Drug; Epinephrine - pharmacology; Female; Heart; Heart Rate; Heart Ventricles - anatomy & histology; Isometric Contraction; Kinetics; Male; Myocardial Contraction - drug effects; Ryanodine - pharmacology; Sarcoplasmic Reticulum - physiology; Smegmamorpha - physiology; Synbranchus marmoratus; Teleostei; Temperature; Tension; Tropical Climate; Ventricular Function
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-007-0166-3

Experiments were carried out to investigate the heart rate of Synbranchus marmoratus after changing the temperature of the water contained in the experimental chamber of the acclimated fish (from 25 to 35°C and from 25 to 15°C). Then, an isometric cardiac muscle preparation was used to test the relative importance of Ca²⁺ released from the sarcoplasmic reticulum and Ca²⁺ influx across the sarcolemma for the cardiac performance under different thermal conditions: 25°C (acclimation temperature), 15 and 35°C. Adrenaline and ryanodine were used to modulate the Ca²⁺ flux through the sarcolemma and the sarcoplasmic reticulum, respectively. Ryanodine reduced the peak tension by approximately 47% at 25°C, and by 53% at 35°C; however, it had no effect at 15°C. A high adrenaline concentration was able to ameliorate the negative effects of ryanodine. Despite increasing the peak tension, adrenaline increased the times necessary for contraction and relaxation. We conclude that the sarcoplasmic reticulum is active in contributing Ca²⁺ to the development of tension at physiological contraction frequencies. The adrenaline-stimulated Ca²⁺ influx is able to increase the peak tension, even after addition of ryanodine, at physiologically relevant temperatures and pacing frequencies.