The effect of a conventional antibiotic penicillin/streptomycin) mixtu
re on the widely used kidney epithelial cell line, LLC-PK1, as investi
gated by measuring growth and intracellular free calcium. Free calcium
concentration was the same in cells cultured for 3 to 7 wk with (''pl
us'') and without (''minus'') antibiotics both at rest and when challe
nged with high (14 mM) external calcium. When exposed to vasopressin,
minus cells exhibited significantly smaller calcium transients than pl
us cells. A similar difference existed for transients elicited by a ca
lcium ionophore, 4-br-A23187. After longer periods of culture (>20 wk)
, minus cells grew slower than plus cells but on reaching confluence (
minus cells took 1 day longer) the morphologies and viabilities were i
ndistinguishable. The finding that culture with pinicillin/streptomyci
n reversibly modified some properties of LLC-PK1 cells, at least partl
y through altered calcium homeostasis, is of importance for workers us
ing this cell model to study drug effects and raises the general possi
bility of similar effects on other cultured cells.