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), 2938 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 ±2.0 mV. Addition of 10 -4mol/1 of dl-propranolol to the basolateral solution rapidly depolarized Vb by 12.1 ± 1.3 mV in 20 sec (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 蜑) occurred in a dose-dependent manner. In the presence of 1 mmol/1 Ba++in basolateral solution, propranolol-induced 蜑 was strongly inhibited. The stilbene derivative DIDS at 1 mmol/1 did not change propranolol-induced 蜑, whereas the elimination of Cl- from the ambient conditions increased propranolol-induced 蜑 蜑. The minimization of the luminal Na+-coupled organic solute transporter by collapsing of the lumen did not inhibit propranolol-induced 蜑 Vb, indicating the lack of effect of propranolol on luminal Na+-coupled transporters. Ouabain at 103- mmol/1 in the bath did not eliminate propranolol-induced 蜑Vb, 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. microelectrode; potas sium channel; in vitro microperfusion; α-adrenergic receptor; barium.
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