Ceramide mediates sustained contraction of smooth muscle cells. C2 ceramide induced a rapid increase in Src kinase activity within 15 s, peaked at 1 min, and was sustained up to 8 min. Contraction and Src kinase activity were inhibited in cells incubated in Ca2+-free medium containing 2 mM EGTA and in cells preincubated with herbimycin A, a Src kinase inhibitor. Immunoblotting using a phosphospecific anti-Src (416Y) antibody showed a ceramide-induced increase in pp60 src tyrosine phosphorylation. Immunoprecipitation using an anti-phosphotyrosine antibody followed by Western immunoblotting using a monoclonal IgG anti-phosphoinositide 3-kinase NH2 terminal-SH2 domain antibody showed a ceramide-induced increase in phosphoinositide 3-kinase (PI 3-kinase) tyrosine phosphorylation at a protein mass corresponding to 85 kDa, the regulatory subunit of PI 3-kinase, which contains the Src kinase binding site. PI 3-kinase phosphorylation was inhibited by herbimycin A and by the PI 3-kinase inhibitors wortmannin and LY-294002. Preincubation of cells with herbimycin A or PI 3-kinase inhibitors also resulted in an inhibition of mitogen-activated protein (MAP) kinase p42 and p44 activities as seen on Western blots. In summary, we found that 1) the maintenance of sustained contraction is dependent on extracellular Ca2+; 2) ceramide activates a nonreceptor tyrosine kinase pathway through activation of pp60 src and PI 3-kinase; and 3) the converging signals are probably through activation of MAP kinase.

Eosinophilic gastroenteritis (EGE) is characterized by eosinophilic infiltration of the digestive organs, most commonly of the stomach and the duodenum. Symptoms of EGE are nonspecific and include nausea, vomiting, abdominal pain, dyspepsia, malabsorption, ascites and weight loss. The various symptoms of EGE depend on its location and the depth of gastrointestinal eosinophil infiltration. We report a case presenting with acute pancreatitis caused by a milk allergy. The patient’s symptoms rapidly improved after treatment with corticosteroids, and he remained symptom-free for more than 20 months by the elimination of cow’s milk from his diet. Serum titers of pancreatic enzymes and total bilirubin simultaneously recovered and blood eosinophil counts normalized. The causative allergens of EGE are too various to detect; however, allergologic exams revealed that a cow’s milk allergy had provoked EGE in our case. Adult-onset cow’s milk allergies are rare; when seen, however, they may present severe complications such as anaphylaxis, gastroenteritis and pancreatitis. When unaccountable gastrointestinal symptoms are observed, EGE caused by food allergies should be included in the differential diagnosis.

We evaluated intracellular pathways responsible for the activation of the small GTP-binding protein Rho p21 in rat pancreatic acini. Intact acini were incubated with or without CCK and carbachol, and Triton X-100-soluble and crude microsomes were used for Western immunoblotting. When a RhoA-specific antibody was used, a single band at the location of 21 kDa was detected. CCK (10 pM–10 nM) and carbachol (0.1–100 μM) dose dependently increased the amount of immunodetectable RhoA with a peak increase occurring at 3 min. High-affinity CCK-A-receptor agonists JMV-180 and CCK-OPE (1–1,000 nM) did not increase the intensities of the RhoA band, suggesting that stimulation of RhoA is mediated by the low-affinity CCK-A receptor. Although an increase in RhoA did not require the presence of extracellular Ca2+, the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid-AM abolished the appearance of the RhoA band in response to CCK and carbachol. The Gq protein inhibitor G protein antagonist-2A (10 μM) and the phospholipase C (PLC) inhibitor U-73122 (10 μM) markedly reduced RhoA bands in response to CCK. The protein kinase C (PKC) activator phorbol ester (10–1,000 nM) dose dependently increased the intensities of the RhoA band, which were inhibited by the PKC inhibitor K-252a (1 μM). The pp60c- src inhibitor herbimycin A (6 μM) inhibited the RhoA band in response to CCK, whereas the calmodulin inhibitor W-7 (100 μM) and the phosphoinositide 3-kinase inhibitor wortmannin (6 μM) had no effect. RhoA was immunoprecipitated with Src, suggesting association of RhoA with Src. Increases in mass of this complex were observed with CCK stimulation. In permeabilized acini, the Rho inhibitor Clostridium botulinum C3 exoenzyme dose dependently inhibited amylase secretion evoked by a Ca2+ concentration with an IC50 of C3 exoenzyme at 1 ng/ml. We concluded that the small GTP-binding protein RhoA p21 exists in pancreatic acini and appears to be involved in the mediation of pancreatic enzyme secretion evoked by CCK and carbachol. RhoA pathways are involved in the activation of PKC and Src cascades via Gq protein and PLC.

No abstract

No abstract