Evidence that basal secretion of relaxin by individual cultured large luteal cells is influenced by mobilization of intracellular calcium: analysis by a reverse hemolytic plaque assay.
Ca2+ redistribution from an intracellular site(s) is a key biochemical event associated with relaxin (RLX) secretion by large luteal cells (LLCs) of porcine origin. However, the functional significance of internal stores of Ca2+ to basal rates of RLX secretion is not well understood. In addition, the identity of the intracellular storage site(s) for Ca2+ within LLCs is not known, nor is it clear if all RLX-releasing LLCs are equally dependent on this pool. In the present study, release of RLX from 24 h cultured luteal cells derived from early pregnant swine was monitored by a reverse hemolytic plaque assay (RHPA). Incubation of cultures in the presence of graded concentrations of thapsigargin (1 nM-1 microM), a plant sesquiterpene lactone that inhibits endoplasmic reticulum Ca(2+)-ATPase and thereby increases cytosolic Ca2+ concentrations, resulted in a dose-related increase in basal RLX secretion. The stimulatory effect of thapsigargin on RLX production was not abrogated by culture in Ca(2+)-free medium. Suppression of Ca2+ release from the endoplasmic reticulum of LLCs, achieved by incubating monolayers in medium containing dantrolene (1-100 microM), resulted in dose-related inhibition of basal RLX release. Taken together, these results suggest that the endoplasmic reticulum serves as a major storage site for Ca2+ redistribution within LLCs and, furthermore, that mobilization from this site is functionally coupled to basal secretion of RLX.
Taylor
M J
MJ
Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Iowa State University, Ames.
Clark
C L
CL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D002478:Cells, Cultured; D003338:Corpus Luteum / Q000166:cytology / Q000378:metabolism*; D003620:Dantrolene / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006462:Hemolytic Plaque Technique; D007424:Intracellular Fluid / Q000378:metabolism; D011247:Pregnancy; D012065:Relaxin / Q000378:metabolism*; D012636:Secretory Rate / Q000187:drug effects; D013268:Stimulation, Chemical; D013552:Swine; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D012065:Relaxin; D003620:Dantrolene; D002118:Calcium