Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias)

Publisher Website
Google Scholar
Abstract
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+ (a cell) 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),a Cl− cell fell from 38±4 to 11±2 mmol·l−1 (n=14),a Na+ cell fell from 37±4 to 17±2 mmol·l−1 (n=12) anda K+ 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 ina Cl− cell was approximately twice as rapid when compared to that ofa Na+ 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) anda K cell 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),a K cell fell only slightly from 135±15 to 112±30 mmol·l−1 (n=4), buta Cl− 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 ina Cl− cell leads to a marked reduction in the apical Cl−-conductance. Furosemide apparently drivesa Cl −/cell to passive distribution and PDbl to the K+ equilibrium potential.<em...

This publication has 37 references indexed in Scilit: