Cholinergic inhibition of urinary acidification by the turtle bladder

The effect of carbachol on urinary acidification by the turtle bladder in vitro was studied. Carbachol inhibited urinary acidification in a dose-dependent fashion, with half maximal inhibition occurring at 4.5 x 10(-5) M. The effect of carbachol on urinary acidification could be totally prevented by atropine, indicating that the inhibition is mediated through a muscarinic receptor. Carbachol inhibited hydrogen ion secretion by decreasing the active proton conductance and not by altering the proton motive force. Carbachol failed to increase passive loss of hydrogen ion from the mucosa. Carbachol increased calcium uptake by the turtle bladder; this increase in calcium uptake could be prevented by pretreatment with atropine, pentobarbital, or lanthanum. Pentobarbital or lanthanum blunted the inhibitory effect of carbachol on hydrogen ion secretion. In the presence of low extracellular calcium (0.2 mM), carbachol failed to increase calcium uptake but caused a significant inhibition of hydrogen ion secretion. In the presence of normal calcium concentration, carbachol caused a significant efflux of calcium. These data demonstrate that carbachol inhibits urinary acidification and suggest that the mechanism of this inhibition may be related, at least in part, to changes in cytosolic calcium.

Functional characterization of drug-induced experimental papillary necrosis

The functional expression of papillary necrosis was investigated with a model of drug-induced papillary necrosis. Bromoethylamine hydrobromide (BEA) administration to rats uniformly resulted in the development of papillary necrosis. All studies were performed 24 hours after BEA administration with the exception of the electrolyte balance studies, which were performed during the 72 hours after the induction of papillary necrosis. GFR was not different between BEA-treated and sham rats. BEA-treated rats had a significantly lower maximal urine osmolality and free water reabsorption than did sham rats. Renal tissue concentrations of sodium, potassium, and water were not different between BEA-treated and sham rats. During water diuresis, free water clearance was not significantly different between the two groups. During sodium bicarbonate administration, maximal bicarbonate reabsorption and urine-blood Pco2 gradient (at comparable urine bicarbonate concentrations) were not significantly different between the two groups. During sodium sulfate infusion, there was no difference in minimum urine pH, ammonium excretion, and net acid excretion between chronically acidotic BEA-injected and sham rats. In rats on "zero" sodium intake, BEA administration resulted in a significant increase in urine flow and sodium excretion, whereas sham rats remained in sodium balance. In rats with restriction of both sodium and chloride, BEA administration resulted in a significant wastage of sodium, chloride, and calcium. There was no difference in potassium excretion between BEA-treated and sham rats during hydropenia, bicarbonate administration, sodium sulfate infusion, or ingestion of a normal potassium diet. When potassium intake was restricted to "zero," BEA-treated rats developed potassium wastage; when potassium intake was increased to 21 mEq/day, BEA-treated rats had a significantly lower potassium excretion than did sham rats. These findings may result from alterations in collecting duct transport, but damage to deep medullary structures may also contribute.