Corticotropin-releasing hormone acts on guinea pig ileal smooth muscle via protein kinase A.
In contraction studies corticotropin-releasing hormone (CRH) was found to relax ileal but not gastric and jejunal smooth muscles of the guinea-pig, precontracted with BaCl2. Under whole-cell patch-clamp conditions, CRH concentration-dependently activated Ca2+-sensitive K+ currents (IK) with ED50=20 pM at 100 nM and ED50=0. 13 pM at 500 nM intracellular Ca2+ respectively. This increase was accompanied by significant hyperpolarization of the cell membranes. CRH 9-41 peptide fragment did not affect IK amplitude, membrane potential or contraction. The CRH-induced increase of IK densities was accelerated in the presence of high intracellular Ca2+ concentrations (500 nM) and was abolished by pretreatment of cells with either ryanodine or thapsigargin, which cause depletion of intracellular Ca2+ stores, as well as in cells treated under conditions prohibiting intracellular Ca2+ store refilling. The effect of CRH on IK was not affected by bath application of various selective inhibitors of membrane-bound phospholipases, protein kinase C, cGMP-dependent protein kinase or Ca2+/calmodulin-dependent protein kinase II, but was effectively antagonized by blockers of protein kinase A (PKA) or adenylyl cyclase. Neither forskolin nor the catalytic subunit of PKA could mimic the effect of CRH on IK. Thus, it was suggested that CRH exerts its relaxing activity on ileal smooth muscle cells via PKA-dependent phosphorylation of some intracellular target coupled to sarcoplasmic reticulum Ca2+ storage machinery.
Duridanova
D B
DB
Department Membrane Ion Channels, Institute of Biophysics, Bulgarian Academy of Sciences, Acad. Georgi Bonchev str., bldg. 21, 1113 Sofia, Bulgaria.
Petkova-Kirova
P S
PS
Lubomirov
L T
LT
Gagov
H
H
Boev
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003346:Corticotropin-Releasing Hormone / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004594:Electrophysiology; D006162:Guanylate Cyclase / Q000378:metabolism; D006168:Guinea Pigs; D007082:Ileum / Q000201:enzymology* / Q000502:physiology; D066298:In Vitro Techniques; D007583:Jejunum / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000201:enzymology* / Q000502:physiology; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D013270:Stomach / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism
D003346:Corticotropin-Releasing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010738:Type C Phospholipases; D006162:Guanylate Cyclase; D002118:Calcium