Fig. 1.

Identification of the minimum extracellular sequence required for ASIC2 acid sensitivity. (A) The ASIC2 protein has two splice variants, ASIC2a and ASIC2b, and the alternatively spliced region consists of one third of the EC domain, TM1, and the intracellular domain with ASIC2b having an extended, novel N-terminus region; ASIC2a is activated by a pH 4 stimulus, whereas ASIC2b is not. (B) Chimeras were constructed in which evermore of the ASIC2b EC domain (black) was replaced with the equivalent ASIC2a sequence (white), and pH sensitivity was tested. Chimeras AB1–AB4 produced a response that was indistinguishable from the endogenous CHO cell current, like that observed in ASIC2b-transfected cells. Chimeras with 45 (AB4.1) and 24 (AB5) amino acids of ASIC2b both responded to pH 4; see text for details. AB9 containing the 31 amino acids that distinguish AB4 (pH insensitive) from AB5 (pH sensitive) was pH insensitive, as were AB10 and AB11 that included evermore ASIC2a sequence. Chimeras AB11-5 and AB11-6 contained the 24 ASIC2b amino acids of AB5 and an additional 5 amino acids (102–106) and (107–111) of ASIC2b, and both responded to a pH 4 stimulus.