Shear stress-induced volume decrease in C11-MDCK cells by BK- / 4

Holtzclaw JD, Liu L, Grimm PR, Sansom SC. Shear stressinduced volume decrease in C11-MDCK cells by BK/ 4. Am J Physiol Renal Physiol 299: F507–F516, 2010. First published June 24, 2010; doi:10.1152/ajprenal.00222.2010.—Large-conductance, calcium-activated potassium channels (BK) are expressed in principal cells (PC) and intercalated cells (IC) in mammalian nephrons as BK/ 1 and BK/ 4, respectively. IC, which protrude into the lumens of tubules, express substantially more BK than PC despite lacking sufficient Na-K-ATPase to support K secretion. We previously showed in mice that IC exhibit size reduction when experiencing high distal flows induced by a high-K diet. We therefore tested the hypothesis that BK/ 4 are regulators of IC volume via a shear stress ( )-induced, calcium-dependent mechanism, resulting in a reduction in intracellular K content. We determined by Western blot and immunocytochemical analysis that C11-Madin-Darby canine kidney cells contained a predominance of BK/ 4. To determine the role of BK/ 4 in -induced volume reduction, we exposed C11 cells to and measured K efflux by flame photometry and cell volume by calcein staining, which changes inversely to cell volume. With 10 dynes/cm, calcein intensity significantly increased 39% and monovalent cationic content decreased significantly by 37% compared with static conditions. Furthermore, the shear-induced K loss from C11 was abolished by the reduction of extracellular calcium, addition of 5 mM TEA, or BK4 small interfering (si) RNA, but not by addition of nontarget siRNA. These results show that BK/ 4 plays a role in shear-induced K loss from IC, suggesting that BK/ 4 regulate IC volume during high-flow conditions. Furthermore, these results support the use of C11 cells as in vitro models for studying BK-related functions in IC of the kidney.