Two lines of MDCK epithelial cells with different volume and ion responses to calcium ionophore A23187.

Madin-Darby canine kidney (MDCK) cells lost volume when exposed to 50 microM calcium ionophore A23187. The ionic mechanism for the volume reduction differed between two types of cells. MDCK1 lost potassium, similar to cells undergoing a volume regulatory decrease in hypotonic medium. MDCK2 predominately lost sodium, as did cells with elevated cyclic AMP or when treated with amiloride. The effects of A23187 and dibutyryl-cyclic AMP on Na and K content and volume suggest that intracellular second messengers can trigger different mechanisms to reduce cell volume.