Parathyroid Ca(2+)-conducting currents are modulated by muscarinic receptor agonists and antagonists.
Parathyroid cells express Ca(2+)-conducting cation currents, which are activated by raising the extracellular Ca2+ concentration ([Ca2+]o) and blocked by dihydropyridines. We found that acetylcholine (ACh) inhibited these currents in a reversible, dose-dependent manner (50% inhibitory concentration approximately equal to 10(-8) M). The inhibitory effects could be mimicked by the agonist (+)-muscarine. The effects of ACh were blunted by the antagonist atropine and reversed by removing ATP from the pipette solution (+)-Muscarine enhanced the adenosine 3',5'-cyclic monophosphate (cAMP) production by 30% but had no effect on inositol phosphate accumulation in parathyroid cells. Oligonucleotide primers, based on sequences of known muscarinic receptors (M1-M5), were used in reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify receptor cDNA from parathyroid poly (A)+ RNA. RT-PCR products displayed > 90% nucleotide sequence identity to human M2- and M4-receptor cDNAs. Expression of M2-receptor protein was further confirmed by immunoblotting and immunocytochemistry. Thus parathyroid cells express muscarinic receptors of M2 and possibly M4 subtypes. These receptors may couple to dihydropyridine-sensitive, cation-selective currents through the activation of adenylate cyclase and ATP-dependent pathways in these cells.
Chang
W
W
Department of Medicine, Veterans Affairs Medical Center, San Francisco, California, USA.
Chen
T H
TH
Pratt
S A
SA
Yen
B
B
Fu
M
M
Shoback
D
D
D000109:Acetylcholine / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001483:Base Sequence; D015220:Calcium Channels / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009116:Muscarine / Q000494:pharmacology*; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D010280:Parathyroid Glands / Q000187:drug effects / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011976:Receptors, Muscarinic / Q000096:biosynthesis* / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D019789:Tetraethylammonium / Q000494:pharmacology
D015220:Calcium Channels; D017931:DNA Primers; D007295:Inositol Phosphates; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D019789:Tetraethylammonium; D001285:Atropine; D009116:Muscarine; D000242:Cyclic AMP; D009543:Nifedipine; D000109:Acetylcholine