Journal of Comparative Physiology B

, Volume 179, Issue 4, pp 469–479

The positive force–frequency relationship is maintained in absence of sarcoplasmic reticulum function in rabbit, but not in rat myocardium

Original Paper


Myocardial calcium handling differs between species, mainly in the relative contribution between the sources for activator calcium. To investigate the role of the myofilaments and intracellular calcium decline in governing the relaxation phase of cardiac muscle, and to elucidate additional determinants of relaxation other than the sarcoplasmic reticulum (SR) at various frequencies within the in vivo range, the present study was performed by altering the calcium handling in rat and rabbit. Trabeculae, iontophoretically loaded with bis-fura-2 to monitor cytoplasmic calcium levels, were subjected to ryanodine and cyclopiazonic acid to inhibit SR function. Simultaneous force and [Ca2+]i measurements were obtained at 1–4 Hz in rabbit and at 4–8 Hz in rat before and after SR inhibition. Inhibition of the SR resulted in increased diastolic and peak calcium levels as well as decreased developed force in both species. Calcium transient amplitude decreased in rat, but increased in rabbit after SR inhibition. Time to peak tension, time from peak tension to 50% relaxation, time to peak calcium, and time from peak calcium to 50% calcium decline were all prolonged. Results suggest that L-type calcium channel current is responsible for increases in calcium with increasing frequency, and that the SR amplifies this effect in response to increased L-type current. The response of the myofilaments to alterations in calcium handling plays a critical role in the final determination of force, and may differ between species. These results imply the balance between force relaxation and calcium decline is significantly different in larger mammals, necessitating a critical re-evaluation of how myocardial relaxation is governed, specifically regarding frequency-dependent activation.


Sarcoplasmic reticulum Frequency Calcium Rabbit Rat 



Developed force


Time to peak tension


Time from peak tension to 50% relaxation


Time from peak tension to 90% relaxation


Time to peak calcium


Time from peak calcium to 50% calcium decline


  1. Backx PH, Ter Keurs HE (1993) Fluorescent properties of rat cardiac trabeculae microinjected with fura-2 salt. Am J Physiol Heart Circ Physiol 264:H1098–H1110Google Scholar
  2. Bassani JW, Bassani RA, Bers DM (1994) Relaxation in rabbit and rat cardiac cells: species-dependent differences in cellular mechanisms. J Physiol 476:279–293PubMedGoogle Scholar
  3. Bassani RA, Altamirano J, Puglisi JL, Bers DM (2004) Action potential duration determines sarcoplasmic reticulum Ca2+ reloading in mammalian ventricular myocytes. J Physiol 559:593–609PubMedCrossRefGoogle Scholar
  4. Bers D (2001) Excitation–contraction coupling and cardiac contractile force, 2nd edn. Kluwer, DordrechtGoogle Scholar
  5. Bers DM (1987) Ryanodine and the calcium content of cardiac SR assessed by caffeine and rapid cooling contractures. Am J Physiol 253:C408–C415PubMedGoogle Scholar
  6. Bers DM (2002) Cardiac excitation–contraction coupling. Nature 415:198–205PubMedCrossRefGoogle Scholar
  7. Bers DM, Perez-Reyes E (1999) Ca channels in cardiac myocytes: structure and function in Ca influx and intracellular Ca release. Cardiovasc Res 42:339–360PubMedCrossRefGoogle Scholar
  8. Bers DM, Stiffel VM (1993) Ratio of ryanodine to dihydropyridine receptors in cardiac and skeletal muscle and implications for E–C coupling. Am J Physiol 264:C1587–C1593PubMedGoogle Scholar
  9. Dean A, Voss D (1999) Design and analysis of experiments. Springer, New YorkCrossRefGoogle Scholar
  10. Hasenfuss G, Maier LS, Hermann HP, Luers C, Hunlich M, Zeitz O, Janssen PM, Pieske B (2002) Influence of pyruvate on contractile performance and Ca(2+) cycling in isolated failing human myocardium. Circulation 105:194–199PubMedCrossRefGoogle Scholar
  11. Hudmon A, Schulman H, Kim J, Maltez JM, Tsien RW, Pitt GS (2005) CaMKII tethers to L-type Ca2+ channels, establishing a local and dedicated integrator of Ca2+ signals for facilitation. J Cell Biol 171:537–547PubMedCrossRefGoogle Scholar
  12. Janssen PM, Periasamy M (2007) Determinants of frequency-dependent contraction and relaxation of mammalian myocardium. J Mol Cell Cardiol 43:523–531PubMedCrossRefGoogle Scholar
  13. Janssen PML, Stull LB, Marban E (2002) Myofilament properties comprise the rate-limiting step for cardiac relaxation at body temperature in the rat. Am J Physiol Heart Circ Physiol 282:H499–H507PubMedGoogle Scholar
  14. Kubalova Z (2003) Inactivation of L-type calcium channels in cardiomyocytes. Experimental and theoretical approaches. Gen Physiol Biophys 22:441–454PubMedGoogle Scholar
  15. Layland J, Kentish JC (1999) Positive force- and [Ca2 +]i-frequency relationships in rat ventricular trabeculae at physiological frequencies. Am J Physiol Heart Circ Physiol 276:H9–H18Google Scholar
  16. Lingrel JB, Kuntzweiler T (1994) Na+, K(+)-ATPase. J Biol Chem 269:19659–19662PubMedGoogle Scholar
  17. Maier LS, Bers DM, Pieske B (2000) Differences in Ca(2+)-handling and sarcoplasmic reticulum Ca(2+)-content in isolated rat and rabbit myocardium. J Mol Cell Cardiol 32:2249–2258PubMedCrossRefGoogle Scholar
  18. Malmqvist UP, Aronshtam A, Lowey S (2004) Cardiac myosin isoforms from different species have unique enzymatic and mechanical properties. Biochemistry 43:15058–15065PubMedCrossRefGoogle Scholar
  19. Monasky MM, Varian KD, Davis JP, Janssen PM (2008a) Dissociation of force decline from calcium decline by preload in isolated rabbit myocardium. Pflugers Arch 456:267–276PubMedCrossRefGoogle Scholar
  20. Monasky MM, Varian KD, Janssen PM (2008b) Gender comparison of contractile performance and beta-adrenergic response in isolated rat cardiac trabeculae. J Comp Physiol [B] 178:307–313Google Scholar
  21. Mulieri LA, Hasenfuss G, Ittleman F, Blanchard EM, Alpert NR (1989) Protection of human left ventricular myocardium from cutting injury with 2, 3-butanedione monoxime. Circ Res 65:1441–1449PubMedGoogle Scholar
  22. Periasamy M, Huke S (2001) SERCA pump level is a critical determinant of Ca(2+)homeostasis and cardiac contractility. J Mol Cell Cardiol 33:1053–1063PubMedCrossRefGoogle Scholar
  23. Philipson KD, Nicoll DA (2000) Sodium-calcium exchange: a molecular perspective. Annu Rev Physiol 62:111–133PubMedCrossRefGoogle Scholar
  24. Pieske B, Maier LS, Bers DM, Hasenfuss G (1999) Ca2+ handling and sarcoplasmic reticulum Ca2+ content in isolated failing and nonfailing human myocardium. Circ Res 85:38–46PubMedGoogle Scholar
  25. Piheiro J, Bates D (2000) Mixed-effects models in S and S-PLUS. Springer, New YorkGoogle Scholar
  26. Raman S, Kelley MA, Janssen PM (2006) Effect of muscle dimensions on trabecular contractile performance under physiological conditions. Pflugers Arch 451:625–630PubMedCrossRefGoogle Scholar
  27. Rodriguez EK, Hunter WC, Royce MJ, Leppo MK, Douglas AS, Weisman HF (1992) A method to reconstruct myocardial sarcomere lengths and orientations at transmural sites in beating canine hearts. Am J Physiol 263:H293–H306PubMedGoogle Scholar
  28. Varian KD, Janssen PM (2007) Frequency-dependent acceleration of relaxation involves decreased myofilament calcium sensitivity. Am J Physiol Heart Circ Physiol 292:H2212–H2219PubMedCrossRefGoogle Scholar
  29. Varian KD, Raman S, Janssen PM (2006) Measurement of myofilament calcium sensitivity at physiological temperature in intact cardiac trabeculae. Am J Physiol Heart Circ Physiol 290:H2092–H2097PubMedCrossRefGoogle Scholar
  30. Zeitz O, Maass AE, Van Nguyen P, Hensmann G, Kogler H, Moller K, Hasenfuss G, Janssen PM (2002) Hydroxyl radical-induced acute diastolic dysfunction is due to calcium overload via reverse-mode Na(+)-Ca(2+) exchange. Circ Res 90:988–995PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of Physiology and Cell Biology, College of MedicineThe Ohio State UniversityColumbusUSA

Personalised recommendations