Regulation of intracellular free Ca2+ by the LH/CG receptor in an established cell line 293 expressing transfected rat receptor.
Luteinizing hormone (LH)/chorionic gonadotropin (CG) receptor (LHR) regulation of intracellular free Ca2+, [Ca2+]i, was studied by spectrofluorometric analysis and digital imaging of intracellularly trapped fura-2 fluorescence in a stable cell line 293 expressing transfected rat LHR. Exposure of the suspensions of 293-LHR cells to human CG (hCG) resulted in single, dose-dependent burst of elevated [Ca2+]i, the maximum being obtained at 0.1-1 microgram hCG/ml. The subconfluent individual 293-LHR cells responded to 1 microgram hCG/ml with either a single or oscillating [Ca2+]i bursts, the appearance of the oscillation being dependent upon the presence of extracellular Ca2+ ([Ca2+]e). 72% of the cells produced oscillation in response to hCG in the presence of [Ca2+]e and only 33% in the absence. Moreover, removal of [Ca2+]e from the incubation medium lowered the elevated basal [Ca2+]i level to or below the prestimulatory level and concomitantly damped out the oscillation, while its readdition without hCG was capable of re-elevating [Ca2+]i level and of gradually restoring the oscillation. The 293-LHR cells exposed to increasing doses of hCG also developed a dose-dependent desensitization of [Ca2+]i increase to renewed hormonal stimulation. The [Ca2+]i bursts within individual 293-LHR cells appeared in particular regions at the cell peripheries rather than distributed uniformly throughout the cytoplasm, pointing to compartmentation of the Ca2+ stores and to a local differences in receptor number in most cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Lakkakorpi
J T
JT
Department of Anatomy, University of Oulu, Finland.
Rajaniemi
H J
HJ
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007424:Intracellular Fluid / Q000378:metabolism; D007668:Kidney; D051381:Rats; D011974:Receptors, LH / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction; D014162:Transfection
D006063:Chorionic Gonadotropin; D011974:Receptors, LH; D011993:Recombinant Fusion Proteins; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2