[biological_process] cardiac muscle cell action potential <sep> cardiac muscle cell action potential involved in contraction <sep> cellular response to mechanical stimulus <sep> magnesium ion transport <sep> membrane repolarization during action potential <sep> membrane repolarization during cardiac muscle cell action potential <sep> positive regulation of potassium ion transmembrane transport <sep> potassium ion import across plasma membrane <sep> potassium ion transmembrane transport <sep> potassium ion transport <sep> protein homotetramerization <sep> regulation of cardiac muscle cell contraction <sep> regulation of heart rate by cardiac conduction <sep> regulation of membrane repolarization <sep> regulation of monoatomic ion transmembrane transport <sep> regulation of skeletal muscle contraction via regulation of action potential <sep> relaxation of cardiac muscle <sep> relaxation of skeletal muscle