36 years after the publication of the important article by Busa and Nuccitelli on the variability of intracellular pH (pH_i) and the interdependence of pH_i and intracellular Ca²⁺ concentration ([Ca²⁺]_i), little research has been carried out on pH_i and calcium signaling. Moreover, the results appear to be contradictory. Some authors claim that the increase in [Ca²⁺]_i is due to a reduction in pH_i, others that it is caused by an increase in pH_i. The reasons for these conflicting results have not yet been discussed and clarified in an exhaustive manner. Variations in pH_i have a significant impact on the increase in [Ca²⁺]_i and hence on some of the basic biochemical mechanisms of calcium signaling. This paper focuses on the possible triggering role of protons, highlighting the mechanisms potentially involved and the open issues that could be clarified by research.

We simulate elementary calcium release events (sparks) in a single calcium release unit in ventricular myocyte. Previously developed and tested electron-conformational model of the stochastic dynamics of RyR-channels is integrated to the calcium dynamics model in the cardiac cell. This approach allows to observe RyRs opening/closing in details on the macromolecular level during the calcium dynamics course. We simulate calcium diffusion in the dyadic space and “domino-like” RyR’s activation during the so-called “calcium induced-calcium release process”. Ca²⁺ sparks initiation, spread and termination are investigated in the computer experiments. Sparks’ initiation and termination rate dependence on the Ca²⁺ diffusion velocity is observed. We show that sarcoplasmic reticulum lumen local depletion and RyR’s stochastic attrition could be the reasons of Ca²⁺ spark termination.