Rapid,non-genomic actions of progesterone and estradiol on steady-state calcium and resting calcium influx in lens epithelial cells

The effects of steroids on the steady-state intracellular [Ca(2+)] ([Ca(2+)](i)) and resting Ca(2+) influx in Fura-2-loaded bovine lens epithelial cells were examined to identify potential rapid, non-genomic actions. When administered in the presence of 1-2 mM extracellular Ca(2+) ([Ca(2+)](o)), 100 micro M progesterone produced large (up to 12-fold) and transient (5 min) increases in [Ca(2+)](i). These effects were abolished in EGTA-containing solutions, and were associated with large increases in the rate at which extracellularly administered Mn(2+) quenched the intracellular Fura signal. Lower concentrations of progesterone (10-100 micro M) produced smaller increases in [Ca(2+)](i) that were concentration dependent, and 17beta-estradiol induced large, rapid and brief increases in [Ca(2+)](i) at 100 nM and smaller oscillations in [Ca(2+)](i) at 10 nM. In cells pretreated with thapsigargin, 100 micro M progesterone produced slower increases in [Ca(2+)](i) that were maintained for several minutes. These results demonstrate rapid non-genomic actions of progesterone and estradiol on resting Ca(2+) influx and [Ca(2+)](i) that may involve specific interactions with a recently discovered steroid-binding protein in the plasma membrane of lens epithelial cells.