[Spontaneous and induced permeability of the tight junctions in the bladder epithelium of the frog Rana temporaria].

The spontaneous and induced alterations in paracellular permeability of the isolated frog urinary bladder were studied. For estimation of the tight junction (TJ) permeability, a fluorescent dye uranine was used. No morphological or functional evidences for the TJ opening were found in the autumn-winter period, both in the control and after the osmotic flow stimulation by 25 mg/ml pituitrine (P) or serosal mannitol (200 mM). In the spring, a spontaneous uranine efflux through the bladder wall from the mucosal solution was found in parallel with an increase in the basal water flow and a decrease in the responses of the bladder to P and serosal hypertonicity. At the same time, the intercellular substance remained to be a barrier for water. In the autumn-winter the TJ opening could be induced by adding sulfhydryl reagents, p-chloromercury-phenyl-sulfonic acid (PCMPS) or N-ethylmaleimide (NEM), to the serosal solution. However, NEM was effective only when added to the mucosal solution. The uranine efflux induced by sulfhydryl reagents was accompanied with a marked hydroosmotic flow in parallel with a diminished sensitivity to P, the barrier properties of intercellular substances were lost. As evidenced by electron microscopy, PCMPS induced a gradual destruction of TJ structures, while certain cytoplasmic structures were not affected. The uranine efflux in the autumn-winter frogs could be induced by an artificial osmotic gradient after preincubation of the bladders in the isotonic solution with P. Some possible intracellular mechanisms causing both spontaneous and induced alterations in the TJ permeability are discussed.