action potentional (myocardial cell)

Last reviewed 01/2018

The action potential of myocardial cells lasts for hundreds of milliseconds (in comparison to depolarization of nerve and skeletal muscle that lasts for only a few milliseconds).

Features of depolarization:

• resting transmembrane potential of myocardial cells - this is about -90 mV (ie the inside of the cell is negative with respect to the extracellular fluid)
• during diastole there is a low intracellular sodium and calcium concentration and high potassium concentration - this is maintained via active transport by the sarcolemma membrane
• depolarization and muscle contraction:
• initially there is a rapid influx of sodium ions - the transmembrane potential increases to about +30mV
• the plateau phase follows in which there appears to be a slower influx of calcium ions
• muscle contraction appears to be initiated by the rise in intracellular calcium concentration. As well as the influx of calcium during the plateau phase, calcium appears to be released from the terminal cysterni of the sarcoplasmic reticulum