The use of lanthanum for intracellular calcium measurements in cultured cells.

The Lanthanum method, used extensively to measure the intracellular Ca content ([Ca]i) of muscle, was adapted for cell culture using the carcinoma line C-4II. Reproducible values of [Ca]i were obtained by atomic absorption spectrophotometry after 30 min of rinsing of monolayer fragments with cold 10 mM LaCl3 in 160 mM Tris-HCl buffer, pH 7.4. [Ca]i values were not influenced by the extracellular Ca concentration, the size of the monolayer fragments or by several culture variables examined. [Ca]i levels were inversely proportional to cell density. The modified La method provides a relatively simple means for [Ca]i measurements and the estimation of net Ca fluxes in and out of cultured cells.