Permissive role of calcium on regulatory volume decrease in freshly isolated mouse cholangiocytes.

ABSTRACT

Calcium (Ca2+) pathways are important in cell volume regulation in many cells, but its role in volume regulatory processes in cholangiocytes is unclear. Thus, we have investigated the role of Ca2+ in regulatory volume decrease (RVD) in cholangiocytes using freshly isolated bile duct cell clusters (BDCCs) from normal mouse. No significant increase in [Ca2+]i was observed during RVD, while ionomycin and ATP showed significant increases. Confocal imaging also showed no significant changes in the levels or distributions of intracellular Ca2+ during RVD. Cell volume study by quantitative videomicroscopy indicated that removal and chelation of extracellular Ca2+ by ethylene glycol-bis (beta-aminoethyl ether)-N,N,N-tetraacetic acid (EGTA) or administration of nifedipine did not affect RVD but verapamil significantly inhibited the RVD. Moreover, Ca2+ agonists or inhibitors of Ca2+ release from intracellular stores had no significant effect on RVD. However, 1,2-bis (2-aminophenoxy) ethane-N,N,N'N'-tetraacetic acid-AM (BAPTA-AM) showed significant decreases in [Ca2+]i and significantly inhibited RVD, which was reversed with coadministration of valinomycin, suggesting that BAPTA-AM-induced inhibition is due to potassium conductance or other cellular processes requiring permissive [Ca2+](i. These findings indicate that an increase in [Ca2+]i or extracellular Ca2+ is not required for RVD but Ca2+ has a permissive role in RVD of mouse cholangiocytes.