Ca2+ transport mediated by a synthetic neutral Ca2+ -ionophore in biological membranes

The effect of a synthetic neutral ligand on the Ca2+ permeability of several biological membranes has been investigated. The ligand had been previously shown to possess Ca2+ -ionophoric activities in artificial phospholipid membranes. The neutral ionophore is able to transport Ca2+ across the membranes of erythrocytes and sarcoplasmic reticulum, when lipophilic anions such as tetraphenylborate and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) are present, presumably to facilitate the diffusion of the charged Ca2+ -ionophore complex across the hydrophobic core of the membrane. In mitochondria, the neutral ionophore promotes the active transport of Ca2+ in response to the negative membrane potential generated by respiration, in the presence of the specific inhibitor of the natural carrier ruthenium red.