EVIDENCE THAT UP-REGULATION OF THE PAROTID NA-K+-2CL(-) COTRANSPORTERBY HYPERTONIC SHRINKAGE IS NOT DUPLICATED BY ISOTONIC SHRINKAGE()

The application of Ca2+ mobilizing secretagogues to rat parotid acini results in a significant decrease in cell volume (15-30%) due to isoto nic salt loss. It is often assumed that the effects of such an isotoni c volume decrease can be mimicked by anisotonic cell shrinkage. We dem onstrate that the Na+-K+-2Cl(-) cotransporter in these cells is up-reg ulated by Ca2+ mobilizing secretagogues as well as by cell shrinkage i n hypertonic media. However, we find that although the protein kinase inhibitors staurosporine (0.3 mu M) and K252a (0.6 mu M) significantly blunt the latter up-regulation, they are without effect on the former . These observations suggest that hypertonic and isotonic shrinkage do not result in the activation of the same intracellular signalling pat hways, and indicate that anisotonic volume perturbations may not provi de good experimental models of physiologic isotonic volume changes.