Enhancement of Ca2+ currents by GHRH and its relation to PKA and [Ca2+]i in human GH-secreting adenoma cells.
The effects of human growth hormone-releasing hormone (hGHRH) on Ca2+ channels were examined in human growth hormone-producing adenoma cells using the perforated whole cell clamp technique. These cells exhibited T- and L-type Ca2+ channel currents, and application of 10(-8) M hGHRH increased the amplitude of both currents. Application of 10(-5) M 8-bromoadenosine 3',5'-cyclic monophosphate also increased T- and L-type currents. Additional application of 10(-8) M hGHRH did not further increase the current amplitudes. Treatment with the Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate (10(-5) M) or H-89 (10(-5) M) inhibited the enhancement of Ca2+ channel currents by hGHRH, as did intracellular injection of protein kinase A (PKA) inhibitor peptide [PKI-(5-24)], indicating that hGHRH increased the amplitude of Ca2+ channel currents through the activation of the adenosine 3',5'-cyclic monophosphate (cAMP)-PKA system. When intracellular Ca2+ concentration ([Ca2+]i) was chelated to < 30 nM with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTAAM), hGHRH failed to increase the Ca2+ channel currents. In this condition, hGHRH activated nonselective cation channels, which revealed that the cAMP-PKA system operated after treatment with BAPTA-AM and that the site of low [Ca2+]i-induced inhibition of hGHRH effects on Ca2+ channels was at a step after PKA activation.
Takei
T
T
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Takano
K
K
Yasufuku-Takano
J
J
Fujita
T
T
Yamashita
N
N
D000236:Adenoma / Q000503:physiopathology*; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments; D010455:Peptides / Q000494:pharmacology; D010911:Pituitary Neoplasms / Q000503:physiopathology*; D013237:Stereoisomerism; D013449:Sulfonamides; D013873:Thionucleotides / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D010446:Peptide Fragments; D010455:Peptides; D013449:Sulfonamides; D013873:Thionucleotides; C518603:protein kinase inhibitor peptide (5-24); D019382:Human Growth Hormone; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; C016957:adenosine-3',5'-cyclic phosphorothioate; D001464:Barium; D004533:Egtazic Acid; D013007:Growth Hormone-Releasing Hormone; D020866:omega-Conotoxin GVIA; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium