[biological_process] cardiac muscle contraction <sep> cellular response to caffeine <sep> detection of calcium ion <sep> intracellular calcium ion homeostasis <sep> negative regulation of potassium ion transmembrane transporter activity <sep> negative regulation of potassium ion transport <sep> negative regulation of ryanodine-sensitive calcium-release channel activity <sep> protein polymerization <sep> Purkinje myocyte to ventricular cardiac muscle cell signaling <sep> regulation of cardiac muscle contraction by regulation of the release of sequestered calcium ion <sep> regulation of cell communication by electrical coupling <sep> regulation of heart rate <sep> regulation of membrane repolarization <sep> regulation of release of sequestered calcium ion into cytosol by sarcoplasmic reticulum <sep> sequestering of calcium ion <sep> striated muscle contraction