Calcium channels, the sodium-calcium exchange and intracellular sodium in the predisposition of the heart to the calcium paradox.

A wide variety of cardiac tissues load with Na+ on exposure to Ca-free fluid. This loading is due to a sustained influx of Na+ through the calcium channels and predisposes the tissues to the changes known as the Calcium Paradox on reperfusion with calcium containing fluid. The cells then load with calcium, most probably via activation of the Na/Ca exchange. This calcium loading may be responsible for the subsequent changes in intracellular pH and cellular metabolism.