Membrane currents associated with TMEM16A protein lacking segment a. A, B. Representative membrane currents associated with transient transfection of HEK-293 cells with TMEM16A(abcd) and TMEM16A(bcd). Experiments were carried out at three free Ca2+ concentrations in the intracellular solution (115, 305, and 685 nM). C, D. Current–voltage relationships from cells expressing (abcd) and (bcd) isoforms, respectively.