Pancreatic neuroendocrine tumors (pNETs) occur due to the abnormal growth of pancreatic islet cells and predominantly develop in the duodenal-pancreatic region. Somatostatinoma is one of the pNETs associated with tumors of pancreatic delta cells, which produce and secrete somatostatin. Limited information is currently available on the pathogenic mechanisms of somatostatinoma. The large-conductance Ca2+-activated K+ (BKCa) channel is expressed in several types of cancer cells and regulates cell proliferation, migration, invasion, and metastasis. In the present study, the functional expression of the BKCa channel was examined in a human somatostatinoma QGP-1 cell line. In QGP-1 cells, outward currents were elicited by membrane depolarization at pCa 6.5 (300 nM) in the pipette solution and inhibited by the specific BKCa channel blocker, paxilline. Paxilline-sensitive currents were detected, even at pCa 8.0 (10 nM) in the pipette solution, in QGP-1 cells. In addition to the alpha and beta 2-4 subunits of the BKCa channel, the novel regulatory g1 subunit (BKCag1) was co-localized with the alpha subunit in QGP-1 cells. Paxilline-sensitive currents at pCa 8.0 in the pipette solution were reduced by the siRNA knockdown of BKCag1. Store-operated Ca2+ entry was smaller in BKCag1 siRNA-treated QGP-1 cells. The proliferation of QGP1 cells was attenuated by paxilline or the siRNA knockdown of BKCag1. These results strongly suggest that BKCag1 facilitates the proliferation of human somatostatinoma cells. Therefore, BKCag1 may be a novel therapeutic target for somatostatinoma. (C) 2020 Elsevier Inc. All rights reserved.