Interrelationships among epidermal Na-K ATPase, developmental stage and length of Rana catesbeiana tadpoles

Skin epithelial transport and structural relationships in naturally metamorphosing Pelobates syriacus

The onset of active Na(+) transport and activated Cl(-) conductance (G(Cl)) across the skin epithelium of Pelobates syriacus was investigated during natural ontogenetic development. Structural features, including band three and Peanut lectin bindings were tested in parallel and structure-function relationships were attempted. The 22 specimens studied were divided into two tadpole, three juvenile, and two adult stages, corresponding to the Taylor-Kollros standard table, in accordance with external morphology of their developmental stage. Onset of transepithelial electrical potential and drop in conductance occurred abruptly, coinciding with metamorphosis climax of tadpoles into juveniles at about stage XXI of development. Amiloride-sensitive Na(+) transport occurred a little later at stage XXIII, followed by the appearance of activated Cl(-) conductance, G(Cl). Parallel structural examination showed that skin MR cells occurred upon metamorphosis, as the tadpole integument transformed into the adult epithelium and could be associated with the occurrence of activated G(Cl). It was not related temporally with the appearance of band three protein in MR cells. Our findings support the association of G(Cl) with MR cells, whereas band three may only be a corollary of G(Cl) and not necessarily essential for its manifestation.

Comparison of the inhibitory effect of ouabain and dihydroouabain on the Na(+)-K+ ATPase from frog skin

1. The effects of ouabain and dihydroouabain (DHO) on Na(+)-K+ ATPase from frog skin were investigated. 2. Ouabain seemed to be a more effective inhibitor, reaching near maximum inhibition at 10(-5) M while DHO reached near maximum at 10(-3) M. 3. Both inhibitors acted within the first few minutes, but ouabain inhibited more strongly over virtually the whole 2 hr considered. 4. Pre-incubation of the enzyme with ATP or Na+ reduced the level of inhibition due to subsequent ouabain or DHO, but preincubation with K+ did not.

Thyroxin specifically stimulates anuran larvae epidermal sodium pump during metamorphosis

1. Sodium pump, measured as K+-dependent, ouabain sensitive pNPPase, but not the non-specific, ouabain insensitive pNPPase, was stimulated by thyroxin in epidermis of tadpoles of Rana perezi. 2. Epidermal K+-pNPPase of thyroxin treated tadpoles was only stimulated in those stages already showing activity and reached levels similar to adult frogs in tadpoles at metamorphic climax.