Urinary Vesicles Research Articles

Effects of internal and external pH on amiloride-blockable Na+ transport across toad urinary bladder vesicles

We have examined the effect of internal and external pH on Na+ transport across toad bladder membrane vesicles. Vesicles prepared and assayed with a recently modified procedure (Garty & Asher, 1985) exhibit large, rheogenic, amiloride-sensitive fluxes. Of the total 22Na uptake measured 0.5-2.0 min after introducing tracer, 80 +/- 4% (mean +/- SE, n = 9) is blocked by the diuretic with a KI of 2 X 10(-8) M. Thus, this amiloride-sensitive flux is mediated by the apical sodium-selective channels. Varying the internal (cytosolic) pH over the physiologic range 7.0-8.0 had no effect on sodium transport; this result suggests that variation of intracellular pH in vivo has no direct apical effect on modulating sodium uptake. On the other hand, 22Na was directly and monotonically dependent on external pH. External acidification also reduced the amiloride-sensitive efflux across the walls of the vesicles. This inhibition of 22Na efflux was noted at external Na+ concentrations of both 0.2 microM and 53 mM. These results are different from those reported with whole toad bladder. A number of possible bases for these differences are considered and discussed. We suggest that the natriferic response induced by mucosal acidification of whole toad urinary bladder appears to operate indirectly through one or more factors, presumably cytosolic, present in whole cells and absent from the vesicles.

Sulfhydryl reagents affect Na+ uptake into toad bladder membrane vesicles

The effect of sulfhydryl reagents on the Na+ permeability mechanisms of toad urinary bladder vesicles was examined. The reagents 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB), iodosobenzoate, and ethylenimine were able to decrease amiloride-inhibited sodium uptake into vesicles when used at low concentrations. When used at higher concentrations these reagents were able to induce large increases in vesicle Na+ permeability that were not sensitive to amiloride. The reagent p-chloro-mercuribenzene sulfonate was able to induce such leaks even at low concentrations. The reagent N-ethylmaleimide was incapable of substantially affecting vesicle Na+ transport in any way. All of the effects observed could be reversed by removing the reagents from the solution surrounding the vesicles. Our results help explain the varied actions of sulfhydryl reagents on intact epithelial tissue.

Developmental changes in the Alimentary canal ofProdenia lituraFabr. (Lepidoptera)

Summary A detailed account of the developmental changes in the alimentary canal of Prodenia litura Fabr. is given. The three primary regions of the gut are distinctly indicated in the larval stage. The mesenteron sends lateral folds on to the posterior stomodaeum and is three times as long as the latter. The proctodaeum is marked by the presence of a muscular pylorus and by the attachment of the malpighian tubules. The whole arrangement of the gut region is disrupted during the pupal period, and rearranged to suit the future imago. The number of malpighian tubules is always six, and each set of the larval malpighian tubules bears a pyriform urinary vesicle at its base. The vesicles lose their identity in the pupa and imago.