Corticotropin-releasing hormone acts on guinea pig ileal smooth muscle via protein kinase A

Abstract

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.

Roles of Protein Kinase A (PKA) and PKC on Corticotropin-Releasing Hormone (CRH)-Induced Elevation of Cytosolic Calcium from Extra- and Intra-cellular Sources

“…To this point, our data are in agreement with published reports showing that CRH induces calcium ion entrance from extra-cellular 2,5,[15][16][17][18] and/or intra-cellular sources 3,6,7,15,16,19,20 .…”

“…It was later shown that the effect of CRH on ACTH secretion is largely dependent on calcium ion influx through activation of voltage-gated L-type Ca ion channels, an effect accompanied by a simultaneous CRH-mediated induction of the expression of these channels 2 . Similarly, the relaxing activity of CRH on ileal smooth muscle cells appears to involve mobilization of calcium ions from intracellular stores within the sarcoplasmic reticulum 3 . This effect of CRH appears to be mediated also by a PKA-dependent signalling pathway.…”

Urocortin relaxes rat tail arteries by a PKA‐mediated reduction of the sensitivity of the contractile apparatus for calcium

“…To date multiple differently regulated adenylate cyclase isoforms have been found (Sunahara et al ., 1996). Such a variety may explain the above mentioned tissue‐dependent diversity of PKA‐dependent signalling by creating spatial and functional compartmentalization of cyclic AMP‐PKA effects (Vegesna & Diamond, 1983; Duridanova et al ., 1999). Despite the intensive studies focused on the cyclic nucleotide‐induced desensitization, its molecular mechanism remains unknown (MacDonald et al ., 2000; Carvajal et al ., 2000).…”

Distribution and chemical coding of corticotropin-releasing factor-immunoreactive neurons in the guinea pig enteric nervous system

“…Co-localization with NOS suggests that the CRF-/NOS-IR myenteric neurons with aboral projections might belong to the population of inhibitory motor neurons to the circular muscle coat and/or descending interneurons that mediate local reflexes. Corelease of CRF from inhibitory motor neurons might be an explanation for the direct action of CRF to relax contractile tension in smooth fibers of the guinea-pig ileum and caecum (Iwakiri et al, 1996;Duridanova et al, 1999) and to suppress small intestinal transit (Williams et al, 1987).…”

“…Co-localization with NOS suggests that the CRF-/NOS-IR myenteric neurons with aboral projections might belong to the population of inhibitory motor neurons to the circular muscle coat and/or descending interneurons that mediate local reflexes. Corelease of CRF from inhibitory motor neurons might be an explanation for the direct action of CRF to relax contractile tension in smooth fibers of the guinea-pig ileum and caecum (Iwakiri et al, 1996;Duridanova et al, 1999) and to suppress small intestinal transit (Williams et al, 1987).Small calretinin-IR uniaxonal neurons comprise 17-24% of the neurons in the myenteric plexus of guinea-pig small intestine (Brookes et al, 1992;Costa et al, 1996). These neurons also express ChAT-IR and are classified as excitatory motor neurons, which innervate the longitudinal muscle layer or as ascending interneurons (Furness, 2000;Brookes, 2001).…”