[Ca2+ participation on the outer surface of the apical membrane of the bladder epithelial cells in the frog in the reaction to antidiuretic hormone].

The ADH effect on the osmotic permeability was studied in experiments on isolated frog urinary bladders. The absence of Ca2+ in the hypotonic solution on the side of the bladder mucous membrane and an increase of its concentration from 0.23 to 11.7 mM/1 did not change the response to the ADH. The removal of Ca2+ from the apical membrane after adding 10(-3) M of EGTA to the mucous membrane solution resulted in an abrupt decrease of cell capabilities to react to the ADH. Ca channel blockers (verapamil, cobalt and nickel ions in 10(-4) M) in the apical plasmic membrane solution lovered the cell response to the ADH. The data obtained indicate that the presence of Ca2+ on the outer surface of the apical plasmic membrane is necessary for the ADH action.