Effect of second messenger systems on oxalate uptake in renal epithelial cells

The oxalate transport system along with protein phosphorylation appears to be deranged in stone formers. This study was undertaken to characterize in LLC-PK₁ cells in culture the effect of altering specific intracellular second messenger systems on oxalate uptake. Cellular uptake experiments were performed at 37°C in buffer [265 mM mannitol, 5 mM NaOH, 5 mM KOH, 10 mM Ca-EGTA, 25 mM HEPES/TRIS, pH=7.4 or in Hank's balanced salt solution (HBSS)] containing 200 M labeled oxalate (1-¹⁴C, 0.3 Ci). Cells were preincubated with DAG (final concentration of 100 M), phorbol myristate acetate (10 M), forskolin (50 M), 8-bromo-cyclic AMP (50 M), trifluoroperazine (20 M) and low molecular weight heparin (1 mg/ml) for 10 min in the presence and absence of the anion transport inhibitor DIDS (100 M) and the effect(s) on oxalate uptake at 10, 25 and 45 min incubation were determined. Chemicals (DAG, forskolin, TPA and 8-bromo-cAMP) which stimulate protein kinase A or C activity resulted in an increased uptake of oxalate while inhibitors of these systems (trifluoroperazine and low molecular weight heparin) resulted in decreased oxalate uptake. The results dernonstrate that oxalate uptake in renal tubular cells is modulated by protein kinase C and A dependent mechanisms.