Heart muscle cells, fluorescence deconvolution micrograph. Fluorescent dyes have been used to highlight cellular structures and proteins: cell nuclei (blue), cardiac actin (green), IP3 receptors (red). Actin is a contractile muscle protein. IP3 receptors are calcium channels. Muscle cell contraction is triggered by rising calcium levels, channelled through receptors like these, and in this case triggering the beating of the heart.
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