Mechanisms of PTH-induced rise in cytosolic calcium in adult rat hepatocytes.
Available data indicate that the liver is a target organ for parathyroid hormone (PTH) and that this effect is most likely mediated by PTH-induced calcium entry into hepatocytes. The present study examined the effects of both PTH-(1-84) and its amino-terminal fragment [PTH-(1-34)] on cytosolic calcium concentration ([Ca2+]i) of hepatocytes and explored the cellular pathways that mediate this potential action of PTH. Both moieties of PTH produced a dose-dependent rise in [Ca2+]i, but the effect of PTH-(1-84) was greater (P < 0.01) than an equimolar amount of PTH-(1-34). This effect required calcium in the medium and was totally [PTH-(1-34)] or partially [PTH-(1-84)] blocked by PTH antagonist ([Nle8,18,Tyr34]bPTH-(7-34)-NH2] and by verapamil or nifedipine. Sodium or chloride channel blockers did not modify this effect. 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), and G protein activator also produced a dose-dependent rise in [Ca2+]i. Staurosporine abolished the effect of TPA, and both staurosporine and calphostin C partially inhibited the effect of PTH. Staurosporine and verapamil together produced greater inhibition of PTH action than each alone. Rp-cAMP, a competitive inhibitor of cAMP binding to the R subunit of protein kinase A, and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), a protein kinase A inhibitor, blocked the effect of both DBcAMP and PTH, but the effect of these agents was greater (P < 0.01) on DBcAMP action. G protein inhibitor and pertussis toxin partially blocked the action of PTH. The data indicate that 1) PTH increases [Ca2+]i of hepatocytes; 2) this action of the hormone is receptor mediated; 3) the predominant pathway for this PTH action is the stimulation of a G protein-adenylate cyclase-cAMP system, which then leads to stimulation of a calcium transport system inhibitable by verapamil or nifedipine or activation of L-type calcium channels; 4) activation of protein kinase C is also involved; and 5) the PTH-induced rise in [Ca2+]i is due, in major parts, to movement of extracellular calcium into the cell.
Division of Nephrology, University of Southern California School of Medicine, Los Angeles 90033.
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Klin
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Smogorzewski
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Khilnani
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Michnowska
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Massry
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D010281:Parathyroid Hormone / Q000494:pharmacology*; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D011506:Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D011506:Proteins; C054296:parathyroid hormone-related protein (1-34); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003994:Bucladesine; D014700:Verapamil; D000242:Cyclic AMP; D009543:Nifedipine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium