CHANGES IN NA+ K+-ATPASE EXPRESSION DURING ADAPTIVE CELL-DIFFERENTIATION IN AVIAN NASAL SALT-GLAND/

Chronic salt stress in ducklings (Anas platyrhynchos) resulted in a su stained accumulation of cyclic AMP in the secretory cells of the nasal salt glands, Adaptive increases in the activity of the Na+/K+-ATPase, measured as ATP hydrolysis rates in freshly isolated tissue, were obs erved after 12 h of salt stress, This change in enzyme activity was as sociated with increases in protein abundance in the alpha- as well as in the beta-subunit of Na+/K+-ATPase and an increase in beta-subunit g lycosylation, We investigated whether the increase in the cytosolic cy clic AMP concentration and the adaptive changes in Na+/K+-ATPase activ ity were causally related, Using an organotypic tissue culture system for salt gland slices from unstressed (naive) ducklings, we produced s imilar changes in Na+/K+-ATPase activity and subunit abundance by trea ting cultured tissue with drugs that elevate cytosolic cyclic AMP leve ls (forskolin, 8-CPT-cAMP) during a 15 h culture period, Protein synth esis assays using cultured tissue revealed that elevations in cytosoli c cyclic AMP level mediate increases in Na+/K+-ATPase subunit abundanc e by slowing down the degradation of ATPase subunits. This increase in the amount of enzyme protein was associated with a significant increa se in Na+/K+-ATPase activity in tissue homogenates, The time course of these changes in cyclic-AMP-treated cultured tissue resembled that ob served in salt-stressed intact animals, indicating that the elevation in cyclic AMP level in salt gland tissue may constitute a portion of t he signalling events ultimately leading to the adaptive increase in Na +/K+-ATPase activity in vivo.