Measurement and modelling of Ca²⁺ waves in isolated rabbit ventricular cardiomyocytes

¹ Glasgow University
² University of Strathclyde

^* To whom correspondence should be addressed. E-mail: g.smith{at}bio.gla.ac.uk.

Submitted on December 22, 2006
Revised on January 30, 2007
Accepted on 29 May 2007

	Abstract

The time course and magnitude of the Ca²⁺ fluxes underlying spontaneous Ca²⁺ waves in single permeabilised ventricular cardiomyocytes were derived from confocal Fluo-5F fluorescence signals. Peak flux rates via the 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 (AIP, 300nM, 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 increased in SERCA V_max and peak RyR2 release flux observed at high cellular [Ca²⁺]. This data supports 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.

Key Words: Ca²⁺ waves, Cardiac, intracellular Ca²⁺