Abstract
KONDO, Y., IGARASHI, Y., KUDO, K., TAKAHASHI, N., ITO, O., INOUE, C.N., FUJIWARA, I. and ABE, K. Electrophysiological Analysis of Effect of Propranolol in Rabbit S2 Proximal Straight Tubule. Tohoku J. Exp. Med., 1994, 172 (1), 29-38-The effect of dl-propranolol on the basolateral membrane potential (Vb) of in vitro microperfused S2 proximal straight tubules of the rabbit kidney was examined using conventional microelectrode techniques. In the steady-state condition, the average of 23 measurements of Vb was -44.8±2.0mV. Addition of 10-4mol/l of dl-propranolol to the basolateral solution rapidly depolarized Vb by 12.1±1.3mV in 20sec (n=15). The same dose of d-isomer of propranolol, which has no beta-blocking effect, also depolarized Vb to a similar extent. The non-selective beta-blocker nadolol, which possesses no membrane stabilising activity, had no effect on Vb. Depolarization of Vb by dl-propranolol in 20 seconds (propranolol-induced ΔVb) occurred in a dose-dependent manner. In the presence of 1mmol/l Ba++ in basolateral solution, propranolol-induced ΔVb was strongly inhibited. The stilbene derivative DIDS at 1mmol/l did not change propranolol-induced ΔVb, whereas the elimination of Cl- from the ambient conditions increased propranolol-induced ΔVb. The minimization of the luminal Na+-coupled organic solute transporter by collapsing of the lumen did not inhibit propranolol-induced ΔVb, indicating the lack of effect of propranolol on luminal Na+-coupled transporters. Ouabain at 10-3mmol/l in the bath did not eliminate propranolol-induced ΔVb, indicating the presence of a target transporter other than Na+/K+ ATPase for propranolol. These results suggest the following; 1) propranolol has a depolarizing effect on Vb in proximal tubule; 2) the effect of propranolol is independent of Cl- transport or Na+-coupled transporters in the luminal membrane; 3) propranolol depolarizes Vb by inhibiting the K+ channel in the basolateral membrane of S2 proximal tubule.
