Microelectrode studies of toad urinary bladder epithelial cells using a novel mounting method.

To optimise the conditions for recording stable membrane potentials, epithelial cells of short-circuited toad bladders were impaled via either their apical or basolateral membranes. Microelectrode impalements via the apical membrane were affected by impalement damage and were typically biphasic, consisting of an initial sharp increase in apical membrane potential (Vsc of around -26 mV), followed by a rapid depolarization of Vsc towards 0 mV in the next 10-20 s. To facilitate basolateral impalement two different methods for mounting bladders were tested. Both mounting methods yielded similar values for Vsc and Ra/Rb (the ratio of apical to basolateral membrane resistance) of around -57 mV and 5, respectively, which were larger than those recorded via the apical membrane and consistent with potential measurements from other tight epithelial tissues. Of the two basolateral mounting methods tested, the agar method gave the most stable impalements, making it possible to use amiloride and Ba2+ to assess for impalement damage. In conclusion, basolateral impalements of agar-mounted toad bladders makes this traditionally difficult tissue amenable to microelectrode studies.