Valinomycin can depolarize mitochondria in intact lymphocytes without increasing plasma membrane potassium fluxes

We have simultaneously measured [3H]methyltriphenylphosphonium+ and 86Rb+ distribution across the mitochondrial and plasma membranes of pig mesenteric lymphocytes. At low concentrations the K+ ionophore valinomycin depolarizes the mitochondria but does not increase Rb+ fluxes across the plasma membrane. At high concentrations of valinomycin the plasma membrane becomes permeable to Rb+ and both TPMP+ and Rb+ distribution give a measure of the K+ diffusion potential.