DISPOSITION OF CALCIUM RELEASE UNITS IN AGAROSE GEL FOR AN OPTIMAL PROPAGATION OF Ca2+ SIGNALS
Manfred H. P. Wussling 1*, Ines Aurich 1, Oliver Knauf 1, Helmut Podhaisky 2 and Hans-Jurgen Holzhausen 3
1 Julius Bernstein Institute of Physiology
2 Institute of Numerical Mathematics
3 Institute of Pathology
* To whom correspondence should be addressed. E-mail: manfred.wussling{at}medizin.uni-halle.de.
Submitted on October 7, 2003
Revised on November 23, 2003
Accepted on 7 September 2004
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Abstract |
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Clusters of calcium-loaded SR vesicles in agarose gel were previously shown to behave as an excitable medium which propagates calcium waves. In a 3D-hexagonal disposition, the distance between neighboring spheres (which may stand for SR vesicles) is constant and the relationship between distance and vesicular protein concentration is expected to be nonlinear. To obtain a distribution of SR vesicles at different protein concentrations as homogeneous as possible, liquid agarose gels were carefully stirred. Electronmicrographs, however, did not confirm the expected relationship between inter-SR vesicle distance and vesicular protein concentration. Light-micrographs, to the contrary, resulted in a protein concentration-dependent disposition of clusters of SR vesicles which is described by a linear function. Stable calcium waves in agarose gel occurred at SR vesicle protein concentrations between 7 and 16 g/l. At lower protein concentrations, local calcium oscillations or abortive waves were observed. The velocities of calcium waves were optimum at about 12 g/l and amounted to nearly 60 µm/s. The corresponding distance of neighboring calcium release units was calculated to be about 4 µm. The results further show that calcium signaling in the described reaction-diffusion system is optimal in a relatively small range of diffusion lengths. A change by ± 2 µm resulted in a reduction of the propagation velocity by 40%. It would appear that (1) the distance between calcium release units (clusters of ryanodine receptors in cells) is a sensitive parameter concerning propagation of Ca2+ signals, and (2) a dysfunction of the reaction-diffusion system in living cells, however, might have a negative effect on the spreading of intracellular calcium signals, thus on the cell's function.
Key Words:
agarose gel, calcium oscillations, calcium waves, clusters of SR vesicles, optimal diffusion lengths
