Inhibition by lanthanum of the calcium paradox phenomenon in rat heart

Injury is sustained by isolated hearts on repletion with calcium after a short period of perfusion with calcium-free medium at 37 degrees. A possible mechanism for the 'calcium paradox' is that exposure to a calcium-fre medium removes extracellular calcium rendering the sarcolemma more permeable to calcium. On calcium repletion, cell injury is triggered by calcium influx. Since lanthanum is known to displace calcium from extracellular pools in heart, it was used in an attempt to modulate the injury of the calcium paradox. The presence of 10 microM lanthanum in the calcium-free perfusion fluid was found to inhibit totally protein release normally produced by subsequent calcium exposure. When lanthanum was added after the calcium-free period and before calcium repletion, protein release was only partly prevented. This shows that a change in membrane properties occurred during the calcium-free perfusion period which could be prevented, but not reversed, by the addition of lanthanum.