Evidence for the presence of calmodulin in fish mucus

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Abstract
Partly purified mucus collected from the skin of 3 species of fish [Sarotherodon mossambicus, Clarias lazera and Salmo gairdneri] contains a protein that, on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, comigrates with bovine brain calmodulin and shows the same Ca-dependent shift in electrophoretic mobility as calmodulin. Fish mucus contains a heat-stable activator of cyclic nucleotide phosphodiesterase; activation is concentration dependent and sensitive to the specific calmodulin inhibitor calmidazolium (R 24571). The presence of calmodulin in fish mucus is further indicated by means of a specific radioimmunoassay. A drop in the Ca concentration of the water induces an increase in the immunoassayable calmodulin concentration of mucus, which indicates that the function of calmodulin in mucus is related to control of permeability of the skin epithelium to water and ions.