Lanthanum affects proliferation and motility of Tetrahymena

Lanthanum (La3+), a Ca-channel blocker, affected proliferation of Tetrahymena concentration-dependently in 2% proteose-peptone (PP) medium. The effect increased with decreasing amount of organic matter (2-0.5% PP). Cell motility was affected slightly in low La3+ concentrations but in high concentrations the cells became motionless with rocking movements; however, most cells regained motility after some hours (restored Ca-homeostasis). Addition of La3+ to the PP media caused formation of a fluffy precipitate which was engulfed by the cells. The capacity to form food vacuoles, was normal in proliferating cells but decreased, or ceased, in growth-inhibited cells. Small refractive granules appeared in all treated cells and most abundantly in growth-inhibited cells. The fine structure of treated cells related to whether they were capable, or not, of proliferation. Electron-dense material (La3+) was abundant in food vacuoles, seen on the surface of cells early after exposure to high concentrations, and present in the dense (small refractive) granules. Hence, La3+ apparently enters the cells.