Intracellular potentials of toad urinary bladder.

Short-circuited urinary bladders of Bufo marinus were impaled with microelectrodes. Intracellular potentials in the order of -80 mV were recorded. On inhibition of apical Na entry they hyperpolarized by about 15 mV and the fractional resistance of the apical membrane increased to near 1.0. These patterns are similar to those of other tight Na transporting amphibian epithelia. On two occasions, stable recordings from a single cell were obtained before and after oxytocin. Intracellular potential and fractional resistance of the apical membrane remained constant despite doubling of Na transport and cellular conductance. This finding suggests that oxytocin stimulates conductive pathways in both, apical and basolateral cell membranes of the toad urinary bladder.