0 0 0 . A simple and sensitive method for separating and detecting the LL, DD and meso diastereomers of the dibasic amino acid diaminopimelic acid (DAP) in the peptidoglycan of Gram-positive bacteria is described.This method is based on reverse phase HPLC separation of chiral derivatives of DAP followed by £uorescence detection of the ophthaldehyde derivatives. Its application to the analyses of cell walls of several Gram-positive bacteria is described, where10 mg or less of dry cells is required.

The rate of transport of bicarbonate was studied in isolated perfused rabbit cortical collecting tubules that were absorbing bicarbonate in vitro. Acetazolamide completely inhibited bicarbonate absorption, as was previously observed with isolated proximal tubules. Therefore, carbonic anhydrase probably is important for bicarbonate absorption in both the proximal tubules and collecting tubules. Inhibition of sodium transport by ouabain or elimination of its transport by completely removing the sodium did not cause a decrease in bicarbonate absorption by the collecting tubules. We previously found that inhibition of sodium transport caused a great decrease in bicarbonate absorption by proximal tubules. Therefore, absorption of bicarbonate is not directly related to sodium transport in collecting tubules, but it probably is related to sodium transport in isolated perfused rabbit proximal tubules. Amiloride inhibited bicarbonate absorption by the collecting tubules consistent with previous observations that the drug inhibits urinary acidification. Although amiloride also inhibits sodium transport and reduces the transepithelial voltage across the collecting tubules, the effect of the drug on bicarbonate transport apparently is independent of the other effects.

No abstract

Rabbit proximal straight tubules from superficial nephrons were perfused in vitro in order to elucidate the mechanism of fluid and bicarbonate absorption. Both processes were greatly inhibited when sodium was replaced in the perfusate and bath by other cations, when ouabain was added to the bath, or when potassium was removed from the bath. We infer that these experimental manipulations inhibit active sodium tranport, and that active sodium transport is a primary process leading to fluid and bicarbonate absorption. Fluid absorption also decreased (but only by 22 to 36%) when bicarbonate was replaced by chloride in the perfusate and bath or when acetazolamide (10(-3)M) was added, suggesting that fluid and sodium transport depend in part on bicarbonate. We infer that the links between fluid, sodiu, and bicarbonate transport are complex and involve at least two mechanisms: 1) a sodium for hydrogen ion exchange mechanism located in the brush border membrane and 2) the transepithelial concentration difference for bicarbonate, which results from its absorption and which acts as an additional driving force for fluid and sodium absorption. Finally, bicarbonate absorption was unaltered when chloride was replaced by nitrate in the perfusate and bath, suggesting that chloride is not necessary for acidification in this nephron segment.

A B S T R A C T We previously reported that rabbit renal cortical collecting tubules can secrete bicarbonate in vitro (i.e., there can be net transport from bath to lumen, causing the concentration in the lumen to increase). Net bicarbonate secretion was observed most often when rabbits had been pretreated with NaHCO3 and were excreting alkaline urine before being killed for experiments. The purpose of the present studies was to elucidate the mechanism involved by testing the effects of ion substitutions and drugs on collecting tubules that were secreting bicarbonate. Acetazolamide inhibited net bicarbonate secretion, suggesting that the process is dependent upon carbonic anhydrase. Net bicarbonate secretion also decreased when sodium in the perfusate and bath was replaced by choline, but not when chloride was replaced by nitrate or methylsulfate. Ouabain had no significant effect. Amiloride caused net bicarbonate secretion to increase. The rate of net secretion did not correlate with transepithelial voltage. The results are compared to those in turtle urinary bladders that also secrete bicarbonate. There are no direct contradictions between the results in the two tissues, i.e., in turtle bladders acetazolamide also inhibited bicarbonate secretion and ouabain had no effect. Nevertheless, it seems unlikely that net secretion of bicarbonate by collecting tubules involves specific exchange for chloride, as has been proposed for turtle bladders, because replacement of chloride by other anions did not inhibit bicarbonate secretion by collecting tubules. It was previously shown that the collecting tubules in vitro also may absorb bicarbonate, especially when the rabbits have been treated with NH4C1 and are excreting acid urine before being killed.