Regulation of TMEM16A Chloride Channel Properties by Alternative Splicing

Expression of TMEM16A protein is associated with the activity of Ca2+-activated Cl- channels. TMEM16A primary transcript undergoes alternative splicing. thus resulting in the generation of multiple isoforms. We have determined the pattern of splicing and assessed the functional properties of the corresponding TMEM16A variants. We found three alternative exons, 6b, 13, and 15, coding for segments of 22, 4, and 26 amino acids, respectively, which are differently spliced in human organs. By patch clamp experiments on transfected cells, we found that skipping of exon 6b changes the Ca2+ sensitivity by nearly 4-fold, resulting in Cl- currents requiring lower Ca2+ concentrations to be activated. At the membrane potential of 80 mV, the apparent half-effective concentration decreases from 350 to 90 nM when the segment corresponding to exon 6b is excluded. Skipping of exon 13 instead strongly reduces the characteristic time-dependent activation observed for Ca2+-activated Cl- channels at positive membrane potentials. This effect was also obtained by deleting only the second pair of amino acids corresponding to exon 13. Alternative splicing appears as an important mechanism to regulate the voltage and Ca2+ dependence of the TMEM16A-dependent Cl- channels in a tissue-specific manner.