Steady-state DPA-capacitive signal changes in response to TX100- and Ca-induced MEND. BHK cells with standard solutions, 8 mM of cytoplasmic ATP, 2 µM extracellular DPA, and 6 µM of cytoplasmic DPA. The DPA- and membrane-related capacitance components are determined by applying voltage pulses to +120 mV for 1.3 s. Membrane capacitance does not depend on voltage, whereas the DPA capacitance becomes negligible at +120 mM. Membrane capacitance is demarcated by a dotted line. (A) TX100-induced MEND. Upon the first application of TX100, MEND amounts to just 50% of the initial cell area. The DPA-capacitive signal, defined by the downward deflections of capacitance, is unchanged by MEND. After a second application of TX100, DPA-capacitive signals increase slowly by 20% with respect to the pre-MEND magnitude. (B) Ca-induced MEND with high (8 mM) ATP and no polyamine in response to two Ca transients. The first Ca transient causes exocytosis without subsequent endocytosis. Cell capacitance increases by 20%, whereas the DPA-capacitive signal increases by nearly threefold. The second Ca transient causes little further exocytosis and a delayed MEND response amounting to 60% of the cell surface. The DPA-capacitive signal decreases in parallel by 20%.