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 wi th the serosal surface of the epithelium clamped at either +50 mV, 0 m V (short-circuited) or -50 mV with respect to the mucosal surface. Fol lowing incubation, portions of tissue were coated with an external alb umin standard and rapidly frozen. Cryosections were freeze-dried and c ell 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). In cubation with vasopressin at +50 mV, and under short-circuit condition s, caused Na uptake without cell swelling or gain in Cl. Clamping at - 50 mV resulted in uptake of water and ions, with considerable variatio n from cell to cell. These variations in cell composition were exacerb ated by vasopressin. The greater the increase in water content, the gr eater 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 othe rs, the gain of Na was predominant and cell K content actually fell, A t -50 mV with ouabain, many of the cells also gained water. As was fou nd in our earlier study with ouabain under short circuit conditions (B owler 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 i n others the K content remained relatively normal. These results indic ate differences between granular cells in the availabilities in the pl asma membranes of ion pathways, either as a consequence of differences in the numbers of such pathways or in their control.