Effects of cellular acidification on ADH-induced intramembrane particle aggregates

8-Bromoadenosine 3',5'-cyclic monophosphate [an analogue of adenosine 3',5'-cyclic monophosphate (cAMP), the intracellular mediator for antidiuretic hormone (ADH) action] induces, in frog urinary bladder, an increase in water permeability that is rapidly and reversibly inhibited by cellular acidification. The effect of CO2 bubbling on the simultaneously observed intramembranous particle aggregates, which probably represent water channels, depended on the time that elapsed after changing medium pH: 3 min of CO2 bubbling depressed the water flux by 70%, whereas the membrane surface occupied by the aggregates remained unchanged. On the contrary, after 9-15 min of CO2 bubbling, both the water flux and the surface area occupied by the aggregates were strongly reduced. These results can be interpreted by accepting two post-cAMP levels of action for cellular acidification: 1) the channels themselves that, as previously suggested by ADH experiments at low temperature, would shift their structure from an "open" to a "closed" state, and 2) the mechanism that controlled the aggregates' plug in and removal.