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

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 (Ca_i) levels in LLC-PK₁ cells. A series of bile acids were compared and found to produce increases in Ca_i in the order: lithocholate sulfate (LCS) > deoxycholate > chenodeoxycholate > lithocholate glucuronide > cholate. LCS (300 M) produces changes in Ca_i (measured using Fura-2) qualitatively similar to those produced by 1 M monomycin, except that only ionomycin is able to release calcium from intracellular stores. The effect on Ca_i is roughly proportional to LCS concentration between 50 and 300 M. The presence of 40 mM Na in the extracellular medium reduces the LCS-induced rise in Ca_i 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 Ca_i, no significant effect of LCS is observed on either cellular Na or K levels, or intracellular pH.Abbreviations used BCECF 2,7-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein - HEPES 4-(-2-hydroxyethyl)-1-piperazine ethanesulfonate - TMA tetramethylammonium - PCA perchloric acid - LCS lithocholate sulfate - EGTA ethylene glycol-bis-(-aminoethyl ether)N,N-tetra-acetic acid - Ca_i intracellular free calcium - pH intracellular pH