EFFECTS OF ADH ON THE APICAL AND BASOLATERAL MEMBRANES OF TOAD URINARY-BLADDER EPITHELIAL-CELLS

Short-circuited urinary bladders from Bufo marinus were supported on t heir apical surface by an agar mounting method and impaled with microe lectrodes via their basolateral membrane. This arrangement provided st able and long-lasting impalements of epithelial cells and yielded reli able membrane potentials and voltage divider ratios (R(a)/R(b)), where R(a) and R(b) are apical and basolateral membrane resistances respect ively. The membrane potential under short-circuit conditions (V-sc,) w as -51.4 +/- 2.2 mV (n = 59), while under open-circuit conditions apic al membrane potential (V-a) and basolateral membrane potential (V-b) w ere -31.0 +/- 2.4 and 59.5 +/- 2.4 mV, respectively. This yields a ''w ell-shaped'' potential profile across the toad urinary bladder, where V-a is inversely related to the rate of transport, I-sc. Antidiuretic hormone (ADH) produced a hyperpolarisation of V-sc and V-b but had no significant effect on V-a. In addition, R(a)/R(b) was significantly in creased by ADH (4.6 +/- 0.5 to 10.2 +/- 3.6). Calculation of individua l membrane resistances following the addition of amiloride showed that ADH produced a parallel decrease in R(a) and R(b) membrane resistance , with the observed increase in R(a)/R(b) being due to a greater perce ntage decrease in R(b) than in R(a). The ability of ADH to effect para llel changes in apical and basolateral membrane conductance helps to m aintain a constant cellular volume despite an increase in transepithel ial transport.