Bile acids increase cellular free calcium in cultured kidney cells (LLC-PK1)

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Abstract
Suspensions of LLC-PK1 cells were used to determine the effect of bile acids on the cellular homeostasis of morganic ions. It is determined that bile acids alter cellular free calcium (Cai) levels in LLC-PK1 cells. A series of bile acids were compared and found to produce increases in Cai in the order: lithocholate sulfate (LCS) > deoxycholate > chenodeoxycholate > lithocholate glucuronide > cholate. LCS (300 μM) produces changes in Cai (measured using Fura-2) qualitatively similar to those produced by 1 μM monomycin, except that only ionomycin is able to release calcium from intracellular stores. The effect on Cai is roughly proportional to LCS concentration between 50 and 300 μM. The presence of 40 mM Na in the extracellular medium reduces the LCS-induced rise in Cai to 20% of that observed in the absence of Na. This effect is specific for Na versus 150 mM extracellular K, Li, or TMA. The effect is not dependent on the Na gradient across the membrane. At concentrations of LCS which induce changes in Cai, no significant effect of LCS is observed on either cellular Na or K levels, or intracellular pH.