Selective K+ ionophore (K0.5 values are 48, 73, 75, 93 and 246 mM for K+, Rb+, Cs+, Na+ and Li+ respectively) that transports K+ across biological and artificial lipid membranes. Inhibits Ca2+-ATPase activity and induces apoptosis through mitochondrial membrane depolarization, caspase-3 activation and phosphatidylserine translocation in vitro.