TMEM16A (also known as anoctamin-1), a plasma membrane protein with eight putative transmembrane segments, has been found as an important constituent of calcium-activated chloride channels (CaCCs). TMEM16A belongs to a protein family that includes other nine members, with TMEM16B (anoctamin-2) also being associated with chloride channel activity. We are investigating the functional role of the different domains of the TMEM16A protein to understand the mechanisms of calcium- and voltage-dependence. TMEM16A gene primary transcript undergoes alternative splicing. There are at least three exons, ex6b, ex13, and ex15, which are differently included/skipped in various organs. Such exons code for segments called (b), (c), and (d), respectively, localized in the intracellular regions of TMEM16A protein. A fourth segment, termed (a), and coding for a large part of TMEM16A amino-terminus, may be skipped when an alternative promoter is used. Interestingly, the inclusion of the 22 amino acid long segment b (ex6b), localized in the amino terminus close to the first transmembrane domain, is associated with decreased calcium sensitivity. Indeed, the half-effective calcium concentration at +80 mV is 90 nM and 350 nM for isoforms (ac) and (abc), respectively. On the other hand, inclusion/skipping of microexon 13, coding for only four amino acids, appears to modulate the voltage-dependent activation of the channel. Analysis of TMEM16A splicing in various adult human organs indicates a coordinated pattern affecting segments (b) and (d). Indeed, organs showing a prevalent inclusion of segment (b) tend to skip segment (d) and viceversa. The role of segment (d), coding for a stretch of 26 amino acids in the first intracellular loop is at present unknown. Alternative splicing of TMEM16A appears to be an important mechanism to regulate the function CaCCs. Further investigation of alternatively spliced segments may provide novel information on the regulation of CaCC activity.