Indexed on: 01 Dec '84Published on: 01 Dec '84Published in: Pflügers Archiv - European Journal of Physiology
Rectal gland tubule (RGT) segements of the spiny dogfish (Squalus acanthias) were perfused in vitro. The effects of inhibitors of known mode of action on transepithelial PD (PDte resistance (Rte), the PD across the basolateral membrane (PDbl), the fractional resistance of this membrane (FRbl), and intracellular activities of Na+, Cl−, K+ (acell) were examined. Furosemide (5·10−4 mol·l−1) reduced PDte from −12±0.7 to −2.3±0.2 mV (n=63), hyperpolarized PDbl from −71±1.3 to −79±0.9 mV (n=59), FRbl decreased from 0.2±0.03 to 0.13±0.01 (n=21),aCl−cell fell from 38±4 to 11±2 mmol·l−1 (n=14),aNa+cell fell from 37±4 to 17±2 mmol·l−1 (n=12) andaK+cell 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 inaCl−cell was approximately twice as rapid when compared to that ofaNa+cell. Ba2+ 0.5 mmol·l−1 (bath) reduced PDte from −7.4±1.2 to −4.1±0.6 mV (n=24), increased Rte from 18±2 to 22±2.5, Ωcm2 (n=14). PDbl depolarized from −75±2 to −48±2 mV (n=42), FRbl increased from 0.2±0.02 to 0.34±0.04 (n=14) andaKcell increased from 143±28 to 188±40 mmol·l−1 (n=4). Ouabain (50·10−6 mol·l−1, bath) reduced PDte from −12±2 to −3±0.5 mV (n=9), Rte increased from 18±3 to 21±3 Ωcm2 (n=5), PDbl depolarized from −67±4 to −26±3 mV (n=14), FRbl increased from 0.23±0.04 to 0.45±0.05 (n=6),aKcell fell only slightly from 135±15 to 112±30 mmol·l−1 (n=4), butaCl−cell 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 Ba2+. The ouabain effects on PDte and PDbl 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 PDte and PDbl. The stilbene disulfonate derivate SITS (≤10−3 mol·l−1, both sides) led to a 36±9% inhibition of PDte. The present data, apart from supporting the cell model proposed in a preceding report, allow the following conclusions: The transient analysis of the furosemide effects is suggestive for a 2 Cl−∶1 Na+ stoichiometry of the carrier. The furosemide induced reduction in FRbl suggests that the fall inaCl−cellleads to a marked reduction in the apical Cl−-conductance. Furosemide apparently drivesaCl−/cell to passive distribution and PDbl to the K+ equilibrium potential.aNa+cell then approaches a minimal value which is close to that present in nonstimulated RGT segments. Ba2+ leads to an increase inaK+cell because it blocks the conductive recycling pathway for this ion. Ouabain does not only inhibit the (Na++K+)-ATPase, it also reduces the K+-conductance of the basolateral membrane. This explains whyaK+cell stays high. The cell PD then is dominated byaCl−cell. The Na+ 2Cl−K+-carrier increasesaCl−cell further and the cell continues to depolarize. Thus, the depolarization of the cell is not a sign of K+ loss but indicative of Cl− gain. In the presence of furosemide ouabain is devoid of any effect on PDbl, suggesting that the Na+2 Cl−K+-carrier is the only quantitatively important source of Na+ entry into the RGT cell.