Effects of voltage clamping on epithelial cell composition in toad urinary bladder studied with x-ray microanalysis

Toad urinary bladder epithelial cells were incubated in Na Ringer's with the serosal surface of the epithelium clamped at either +50 mV, 0 mV (short-circuited) or -50 mV with respect to the mucosal surface. Following incubation, portions of tissue were coated with an external albumin standard and rapidly frozen. Cryosections were freeze-dried and cell composition determined by x-ray microanalysis. Cell water and ion contents were unaffected when tissues were short-circuited rather than clamped close to their open-circuit potential difference (+50 mV). Incubation with vasopressin at +50 mV, and under short-circuit conditions, caused Na uptake without cell swelling or gain in Cl. Clamping at -50 mV resulted in uptake of water and ions, with considerable variation from cell to cell. These variations in cell composition were exacerbated by vasopressin. The greater the increase in water content, the greater the rise in cell Cl. However, there was no consistent pattern to the associated changes in cation contents. Most cells gained some Na. In some cells, this gain was accompanied by an increase in K. In others, the gain of Na was predominant and cell K content actually fell. At -50 mV with ouabain, many of the cells also gained water. As was found in our earlier study with ouabain under short circuit conditions (Bowler et al., 1991), there was considerable variation in the extent of the Na gain and K loss; some cells were largely depleted of K while in others the K content remained relatively normal. These results indicate differences between granular cells in the availabilities in the plasma membranes of ion pathways, either as a consequence of differences in the numbers of such pathways or in their control.