Cell swelling increases intracellular free [Ca] in cultured toad bladder cells.

We examined the effect of cell swelling on intracellular free calcium concentration ([Ca]i) in cultured toad bladder cells (TB-M) grown as a polarized monolayer on collagen-coated filters. [Ca]i was measured by use of fura-2, fluorescence microscopy, and simple video imaging. In preliminary experiments we determined that reducing ionic strength by 15% had no effect on the Kd of fura-2, indicating that the dye could be used to examine the effects of cell swelling on [Ca]i. Reducing the osmolality of the serosal bathing medium by 15% caused [Ca]i to increase within 10 s from 97 +/- 9 to 354 +/- 88 nM (n = 5). By 2 min [Ca]i had declined to 163 +/- 22 nM. The increase in [Ca]i was not caused by a fall in Na concentration ([Na]) because isosmotic reduction of serosal [Na] did not result in an increase in [Ca]i. The swelling-induced increase in [Ca]i could be abolished by lowering serosal [Ca] to 200 nM and by addition of lanthanum. The calcium-channel blockers nitrendipine and verapamil also inhibited the swelling-induced increase in [Ca]i, although to different degrees. These experiments demonstrate that swelling of cultured toad bladder cells results in a significant increase in [Ca]i by enhancing the rate of calcium entry across the basolateral membrane, possibly through a calcium channel.