EAVK segment "c" sequence confers Ca-dependent changes to the kinetics of full-length human Ano1.

Anoctamin1 (Ano1 and TMEM16A) is a calcium-activated chloride channel specifically expressed in the interstitial cells of Cajal (ICC) of the gastrointestinal tract muscularis propria. Ano1 is necessary for normal electrical slow waves and ICC proliferation. The full-length human Ano1 sequence includes an additional exon, exon "0," at the NH terminus. Ano1 with exon 0 [Ano1] had a lower EC for intracellular calcium ([Ca]) and faster chloride current () kinetics. The Ano1 alternative splice variant with segment "c" encoding exon 13 expresses on the first intracellular loop four additional amino acid residues, EAVK, which alter at low [Ca] Exon 13 is expressed in 75-100% of Ano1 transcripts in most human tissues but only 25% in the human stomach. Our aim was to determine the effect of EAVK deletion on Ano1 parameters. By voltage-clamp electrophysiology, we examined in HEK293 cells transiently expressing Ano1 with or without the EAVK sequence [Ano1ΔEAVK]. The EC values of activating and deactivating for [Ca] were 438 ± 7 and 493 ± 9 nM for Ano1 but higher for Ano1ΔEAVK at 746 ± 47 and 761 ± 26 nM, respectively. Meanwhile, the EC values for the ratio of instantaneous to steady-state were not different between variants. Congruently, the time constant of activation was slower for Ano1ΔEAVK than Ano1 currents at intermediate [Ca] These results suggest that EAVK decreases the calcium sensitivity of Ano1 current activation and deactivation by slowing activation kinetics. Differential expression of EAVK in the human stomach may function as a switch to increase sensitivity to [Ca] via faster gating of Ano1. Calcium-activated chloride channel anoctamin1 (Ano1) is necessary for normal slow waves in the gastrointestinal interstitial cells of Cajal. Exon 0 encodes the NH terminus of full-length human Ano1 [Ano1], while exon 13 encodes residues EAVK on its first intracellular loop. Splice variants lack EAVK more often in the stomach than other tissues. Ano1 without EAVK [Ano1ΔEAVK] has reduced sensitivity for intracellular calcium, attributable to slower kinetics. Differential expression of EAVK may function as a calcium-sensitive switch in the human stomach.