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Measurement and Modeling of Ca²⁺ Waves in Isolated Rabbit Ventricular Cardiomyocytes

N. MacQuaide ^*, J. Dempster  and G. L. Smith ^*

^* Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, United Kingdom; and Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, United Kingdom

Correspondence: Address reprint requests to G. L. Smith, Tel.: 44-141-330-5963; Fax: 44-141-330-4612; E-mail: g.smith{at}bio.gla.ac.uk.

The time course and magnitude of the Ca²⁺ fluxes underlying spontaneous Ca²⁺ waves in single permeabilized ventricular cardiomyocytes were derived from confocal Fluo-5F fluorescence signals. Peak flux rates via the sarcoplasmic reticulum (SR) release channel (RyR2) and the SR Ca²⁺ ATPase (SERCA) were not constant across a range of cellular [Ca²⁺] values. The Ca²⁺ affinity (K_mf) and maximum turnover rate (V_max) of SERCA and the peak permeability of the RyR2-mediated Ca²⁺ release pathway increased at higher cellular [Ca²⁺] loads. This information was used to create a computational model of the Ca²⁺ wave, which predicted the time course and frequency dependence of Ca²⁺ waves over a range of cellular Ca²⁺ loads. Incubation of cardiomyocytes with the Ca²⁺ calmodulin (CaM) kinase inhibitor autocamtide-2-related inhibitory peptide (300 nM, 30 mins) significantly reduced the frequency of the Ca²⁺ waves at high Ca²⁺ loads. Analysis of the Ca²⁺ fluxes suggests that inhibition of CaM kinase prevented the increases in SERCA V_max and peak RyR2 release flux observed at high cellular [Ca²⁺]. These data support the view that modification of activity of SERCA and RyR2 via a CaM kinase sensitive process occurs at higher cellular Ca²⁺ loads to increase the maximum frequency of spontaneous Ca²⁺ waves.