Force-frequency relation in frog-ventricle is dependent on the direction of sodium/calcium exchange in diastole

S. Subramani, S. Balakrishnan, T. Jyoti, S. Sathishkumar, Abrar Alvi Mohammed, S. Arasan, C. Vijayanand

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Abstract

Aim: Force of contraction increases with stimulus-frequency in mammalian and amphibian hearts under control conditions. Here, we have analysed the mechanism of the force-frequency relation (FFR) in frog-ventricle. Methods: Circular strips of frog-ventricle were subjected to field-stimulation with frequencies in the range 0.03-0.2 Hz and force recorded on a chart-recorder. In another protocol, varying rest-periods were imposed while the preparation beat steadily at 0.2 Hz and the effect of rest on post-rest beat amplitude was noted. Results: Under control conditions, a positive FFR and a rest-induced decay of contraction amplitude (RID) were seen in the frequency range 0.03-0.2 Hz. With cadmium, nifedipine, nickel (40 μmol L-1), ryanodine and adrenaline (all drugs at 10 μmol L-1 concentration, except nickel), the positive FFR and RID seen under control conditions persisted. When the bathing solution contained ouabain (10 μmol L-1) or low external sodium (40 mmol L-1), or high external calcium (5 mmol L-1), the FFR turned negative in the frequency range stated above and there were rest-induced potentiations (RIP). Conclusion: When the conditions favour a net leak of calcium in diastole from intracellular stores via the calcium-extrusive mode of sodium-calcium exchanger (NCX), FFR is positive. An increase in frequency lessens the diastolic interval and therefore the diastolic calcium leak, thereby augmenting force. On the other hand, interventions which favour the calcium-acquisitive mode of NCX during diastole, changed the pattern of RID to RIP and converted FFR from positive to negative. With net diastolic calcium uptake, there is better store-filling and therefore higher force at lower frequencies.

Original languageEnglish
Pages (from-to)193-202
Number of pages10
JournalActa Physiologica Scandinavica
Volume185
Issue number3
DOIs
StatePublished - 1 Nov 2005

Keywords

  • Calcium-handling
  • Cardiac muscle
  • Force-frequency relation
  • Frog-ventricle
  • Sodium-calcium exchanger

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    Subramani, S., Balakrishnan, S., Jyoti, T., Sathishkumar, S., Mohammed, A. A., Arasan, S., & Vijayanand, C. (2005). Force-frequency relation in frog-ventricle is dependent on the direction of sodium/calcium exchange in diastole. Acta Physiologica Scandinavica, 185(3), 193-202. https://doi.org/10.1111/j.1365-201X.2005.01487.x