Potential difference responses due to K +, Na + and Cl − changes in Bullfrog antrum with and without HCO 3−

Abstract

The effect of changing [K +], [Na +] and [Cl −] in nutrient solution was studied in bullfrog antrum with and without HCO 3 − in nutrient. In 25 mM HCO 3 − (95% O 2/5% CO 2) and in zero HCO 3 − (100% O 2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K + or from 81 to 8.1 mM Cl − gave a decrease 10 min later in transmucosal PD (nutrient became more negative) — a normal response. These responses were less in zero than in 25 mM HCO 3 −. A decrease from 102 to 8 mM Na + decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO 3 −. In contrast, change from 4 to 40 mM K + gave initial anomalous PD response and change from 102 to 8 mM Na +, initial normal PD response with either zero or 25 mM HCO 3 −. Both responses were associated with (Na + + K +)-ATPase pump and were greater in zero than in 25 mM HCO 3 −. Initial PD increases in zero HCO 3 − are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO 3 − modifies conductance pathways of nutrient membrane.