Corticotropin-releasing hormone stimulation of Ca2+ entry in corticotropes is partially dependent on protein kinase A.
The modulation of membrane excitability and cytosolic Ca2+ levels by corticotropin-releasing hormone (CRH), (Bu)2cAMP (dBcAMP), and forskolin was examined in enriched populations of cultured rat anterior pituitary corticotropes. CRH (2 or 20 nM), dBcAMP (1 and 5 mM), and forskolin (10 microM) caused a long lasting membrane depolarization accompanied by the onset of cell firing in quiescent cells or by increased firing frequency in spontaneously active cells. All three substances also increased cytosolic Ca2+ levels by increasing the frequency and amplitude of cytosolic Ca2+ transients. These results are consistent with a previous report on human corticotrope tumor cells demonstrating that CRH-induced action potentials lead to enhancement of Ca2+ uptake through voltage-dependent Ca2+ channels. Preincubation with (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), an inhibitor of cAMP-dependent protein kinase A, did not inhibit the CRH-induced depolarization, but attenuated the CRH-induced increase in action potential frequency. H-89 inhibited CRH-induced changes in cytosolic Ca2+ by 69% in spontaneously active cells and by 83% in quiescent cells. In contrast, H-89 completely abolished the effects of dBcAMP and forskolin on membrane potential and cytosolic Ca2+ levels. It is concluded that activation of protein kinase A mediates all of the response to dBcAMP and forskolin, but only a portion of the response to CRH. The portion of the response to CRH that is resistant to H-89 is mediated by a cAMP-independent mechanism.
Kuryshev
Y A
YA
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77555-0641, USA.
Childs
G V
GV
Ritchie
A K
AK
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D004594:Electrophysiology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides
D007546:Isoquinolines; D013449:Sulfonamides; D005576:Colforsin; D003994:Bucladesine; D003346:Corticotropin-Releasing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium