The use of a fluorescent probe to monitor alterations in trans-membrane potential in single cell suspensions

When single cell suspensions of thymic lymphocytes, splenic lymphocytes and platelets are equilibrated with a carbocyanine dye, 3,3′-dipnetyloxacarbocyanine idoide the fluorescence emission intensity is related to the trans-membrane potential. Addition of valinomycin to these cells provokes a net potassium efflux, and membrane hyperpolarisation, which is reflected as a decrease in fluorescence intensity. Increasing the extra-cellular potassium concentration, and thus decreasing the concentration gradient of that ion across the membrane, reduces the change in fluorescence intensity induced by valinomycin.