Gonadotropin releasing hormone stimulates calmodulin redistribution in rat pituitary

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Abstract
Calcium (Ca2+) seems to have an informational role in many tissues. In particular, it fulfills the requirements of a second messenger for gonadotropin releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release from the pituitary gonadotrope (see ref. 1 for review). Very little is known about the effect of this ion on intracellular targets or the mechanism by which Ca2+ mobilization stimulates LH release. One intracellular target for Ca2+ is calmodulin, a ubiquitous intracellular Ca2+ receptor that has been shown to modulate many cellular functions, including cyclic nucleotide and glycogen metabolism, protein phosphorylation, microtubule assembly and disassembly, a Ca2+ flux, and the activities of NAD kinase, tryptophan 5' monooxidase and phospholipase A2 (see refs 2-5 for reviews). We have now used a specific and sensitive radioimmunoassay to determine the quantity and distribution of calmodulin in the gonadotrope before and during GnRH-stimulated LH release. The data indicate that GnRH stimulates redistribution of calmodulin from the cytosol to the plasma membrane and suggest that the molecule may have a role in the mechanism of stimulus-secretion coupling.