| Summary: | Rectal gland tubule (RGT) segments of the spiny dogfish (Squalus acanthias) were perfused in vitro. The effects of inhibitors of known mode of action on transepithelial PD (PD te resistance (R te ), the PD across the basolateral membrane (PD bl ), the fractional resistance of this membrane (FR bl ), and intracellular activities of Na + , Cl − , K + (a cell) were examined. Furosemide (5·10 −4 mol·l −1 ) reduced PD te from −12±0.7 to −2.3±0.2 mV (n=63), hyperpolarized PD bl from −71±1.3 to −79±0.9 mV (n=59), FR bl decreased from 0.2±0.03 to 0.13±0.01 (n=21),a cellCl − fell from 38±4 to 11±2 mmol·l −1 (n=14),a cellNa + fell from 37±4 to 17±2 mmol·l −1 (n=12) anda cellK + was constant [113±14 vs. 117±15 mmol·l −1 (n=6)]. Furosemide exerted its effects within some 20–40 s. Its action was completely reversible. Analysis of the time courses revealed that the furosemide induced initial fall ina cellCl − was approximately twice as rapid when compared to that ofa cellNa + . Ba 2+ 0.5 mmol·l −1 (bath) reduced PD te from −7.4±1.2 to −4.1±0.6 mV (n=24), increased R te from 18±2 to 22±2.5, Ωcm2 (n=14). PD bl depolarized from −75±2 to −48±2 mV (n=42), FR bl increased from 0.2±0.02 to 0.34±0.04 (n=14) anda cellK increased from 143±28 to 188±40 mmol·l −1 (n=4). Ouabain (50·10 −6 mol·l −1 , bath) reduced PD te from −12±2 to −3±0.5 mV (n=9), R te increased from 18±3 to 21±3 Ωcm2 (n=5), PD bl depolarized from −67±4 to −26±3 mV (n=14), FR bl increased from 0.23±0.04 to 0.45±0.05 (n=6),a cellK fell only slightly from 135±15 to 112±30 mmol·l −1 (n=4), buta cellCl − increased from 35±12 to 111±37 mmol·l −1 (n=3). These effects of ouabain were slow when compared to those exerted by furosemide or Ba 2+ . The ouabain effects on PD te and PD bl were completely prevented if furosemide was applied first. Amiloride (≤10−3 mol·l −1 , both sides), and anthracene-9-carboxylate (≤10 −3 mol·l −1 , lumen) were devoid of effects on PD te and PD bl . The stilbene disulfonate derivate SITS (≤10 −3 mol·l −1 , both sides) led to a 36±9% inhibition of PD ...
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