Effect of agents that alter cell calcium and microfilaments on CO2 stimulated H+ secretion in the turtle bladder.

CO2 addition to the serosal solution of turtle bladder stimulates H+ secretion. This stimulation of H+ secretion is thought to be mediated, at least in part, by exocytosis of vesicles containing H+ pumps that are inserted in the plasma membranes. In other systems, exocytosis is regulated by cell calcium and microfilaments. We, therefore, investigated the role of cell calcium and microfilaments on CO2 stimulation of H+ secretion. Trifluperazine and calmidazolium, inhibitors of calmodulin, did not alter base line H+ secretion, but significantly inhibited CO2 stimulation of H+ secretion. Lanthanum, an agent that displaces membrane bound calcium, also significantly inhibited CO2 stimulated H+ secretion when added to the mucosal solution. Removal of serosal Na, a maneuver that presumably changes cytosolic calcium via inhibition of Na-Ca exchange, decreased both base line as well as CO2 stimulated H+ secretion. In bladders treated with the microfilament disrupting agent cytochalasin B, there was inhibition of both base line and CO2 stimulated H+ secretion. In summary, agents that alter cell calcium or the cytoskeleton, inhibit CO2 stimulated H+ secretion, a finding compatible with the suggestion that exocytosis plays a role in this phenomenon.