Molecular and functional characterization of ERG, KCNQ, and KCNE subtypes in rat stomach smooth muscle

Contribution of K+ channels derived from the expression of ERG, KCNQ, and KCNE subtypes, which are responsible for rapidly and slowly activating delayed rectifier K+ currents (I-Kr and I-Ks, respectively) in cardiac myocytes, to membrane currents was examined in stomach circular smooth muscle cells (SMCs). The region-qualified multicell RT-PCR showed that ERG1/KCNE2 transcripts were expressed in rat stomach fundus and antrum SMCs and that KCNQ1/KCNE1 transcripts were expressed in antrum but not fundus. Western blotting and immunocytochemical analyses indicate that ERG1 proteins were substantially expressed in both regions, whereas KCNE1 proteins were faintly expressed in antrum and not in fundus. Both I-Kr- and I-Ks-like currents susceptible to E-4031 and indapamide, respectively, were identified in circular SMCs of antrum but only I-Kr-like current was identified in fundus. It is strongly suggested that I-Kr- and I-Ks-like currents functionally identified in rat stomach SMCs are attributable to the expression of ERG1/KCNE2 and KCNQ1/KCNE1, respectively. The membrane depolarization by 1 muM E-4031 indicates the contribution of K+ channels encoded by ERG1/KCNE2 to the resting membrane potential in stomach SMCs.