Human chorionic gonadotropin (hCG) increases cytosolic free calcium in adult rat Leydig cells

• Published in: Cell calcium (Edinburgh) Vol. 15; no. 5; pp. 349 - 355
• Main Authors: Kumar, S., Blumberg, D.L., Canas, J.A., Maddaiah, V.T.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier India Pvt Ltd 01.05.1994; Elsevier
• Subjects: Animals; Biological and medical sciences; Calcium - metabolism; Cell physiology; Chorionic Gonadotropin - pharmacology; Cyclic AMP - metabolism; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Leydig Cells - drug effects; Male; Molecular and cellular biology; Rats; Rats, Sprague-Dawley; Signal transduction; Calcium; Rat; Free ion; Rodentia; Gonadotropin; Glycoprotein hormone; Cytosol; HCG; Leydig cell; Signal transduction; Vertebrata; Regulation(control); Mammalia; Membrane transport
• ISSN: 0143-4160; 1532-1991
• DOI: 10.1016/0143-4160(94)90010-8

Regulation of steroidogenesis by luteinizing hormone is mediated by cAMP and calcium. We have investigated changes in cytosolic free calcium ([Ca 2+] i) in Leydig cells by using Fura-2 as the fluorescent calcium indicator. Purified Leydig cells were plated on polylysine coated glass coverslips, cultured for 24 h in DMEM F12 and loaded with Fura-2 at 37°C. [Ca 2+] i measurements were made fluorometrically by placing coverslips into 3 ml cuvettes with PBS + calcium. Addition of hCG increased [Ca 2+] i gradually after a lag of about 2–3 min and plateaued by 5–6 min. The plateau level was sustained for at least 15 min. Absence of external Ca 2+ in the medium or presence of diltiazem or nicardipine or cobalt chloride abolished the rise. Addition of BAY K 8644 or KCl caused a small but significant increase of [Ca 2+] i. 8-Br-cAMP, forskolin or cholera toxin produced a gradual rise in [Ca 2+] i that plateaued after 5–6 min similar to that observed with hCG. The action of hCG was inhibited by protein kinase A inhibitor (20-residues peptide) but not by protein kinase C inhibitor (staurosporine). We conclude that binding of hCG to its receptors would transmit the signal through G proteins to adenylyl cyclase to increase cAMP which would increase Ca 2+ influx into cytosol across plasma membrane Ca 2+ channels. Therefore, it appears that the primary action of hCG is to increase cytosolic cAMP which would then regulate [Ca 2+] i as well as steroidogenesis.