An endothelium-dependent contraction in canine mesenteric artery caused by caffeine

The glycerophosphoinositols: cellular metabolism and biological functions

The glycerophosphoinositols are cellular products of phospholipase A(2) and lysolipase activities on the membrane phosphoinositides. Their intracellular concentrations can vary upon oncogenic transformation, cell differentiation and hormonal stimulation. Specific glycerophosphodiester phosphodiesterases are involved in their catabolism, which, as with their formation, is under hormonal regulation. With their mechanisms of action including modulation of adenylyl cyclase, intracellular calcium levels, and Rho-GTPases, the glycerophosphoinositols have diverse effects in multiple cell types: induction of cell proliferation in thyroid cells; modulation of actin cytoskeleton organisation in fibroblasts; and reduction of the invasive potential of tumour cell lines. More recent investigations include their effects in inflammatory and immune responses. Indeed, the glycerophosphoinositols enhance cytokine-dependent chemotaxis in T-lymphocytes induced by SDF-1alpha-receptor activation, indicating roles for these compounds as modulators of T-cell signalling and T-cell responses.

Unaltered caffeine-induced relaxation in the aorta of stroke-prone spontaneously hypertensive rats (SHRSP)

Caffeine-induced relaxation was studied in aortic segments from Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Although acetylcholine-induced endothelium-dependent relaxation was impaired in preparations from SHRSP, the relaxation induced by caffeine was identical in both groups. In addition, caffeine-induced relaxation was not affected by removal of the endothelium in either group. The relaxation induced by N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (db-cAMP), a membrane-permeable analog of adenosine 3':5'-cyclic monophosphate (cAMP), was identical in both groups. No significant difference was observed in the increase in cAMP content induced by caffeine in the aortic smooth muscle between the groups, although the basal content was significantly higher in preparations from SHRSP. These results suggest that the relaxation induced by caffeine in these preparations is brought about by its direct effect on smooth muscle and that the response of the smooth muscle to caffeine, including cAMP production, is not altered in preparations from SHRSP compared with those from WKY.

The effect of 24R,25-(OH)(2)D(3) on protein kinase C activity in chondrocytes is mediated by phospholipase D whereas the effect of 1alpha,25-(OH)(2)D(3) is mediated by phospholipase C

1alpha,25-(OH)(2)D(3) regulates protein kinase C (PKC) activity in growth zone chondrocytes by stimulating increased phosphatidylinositol-specific phospholipase C (PI-PLC) activity and subsequent production of diacylglycerol (DAG). In contrast, 24R,25-(OH)(2)D(3) regulates PKC activity in resting zone (RC) cells, but PLC does not appear to be involved, suggesting that phospholipase D (PLD) may play a role in DAG production. In the present study, we examined the role of PLD in the physiological response of RC cells to 24R,25-(OH)(2)D(3) and determined the role of phospholipases D, C, and A(2) as well as G-proteins in mediating the effects of vitamin D(3) metabolites on PKC activity in RC and GC cells. Inhibition of PLD with wortmannin or EDS caused a dose-dependent inhibition of basal [3H]-thymidine incorporation by RC cells and further increased the inhibitory effect of 24R,25-(OH)(2)D(3). Wortmannin also inhibited basal alkaline phosphatase activity and [35]-sulfate incorporation and decreased the stimulatory effect of 24R,25-(OH)(2)D(3). This inhibitory effect of wortmannin was not seen in cultures treated with the PI-3-kinase inhibitor LY294002, verifying that wortmannin affected PLD. Wortmannin also inhibited basal PKC activity and partially blocked the stimulatory effect of 24R,25-(OH)(2)D(3) on this enzyme activity. Neither inhibition of PI-PLC with U73122, nor PC-PLC with D609, modulated PKC activity. Wortmannin had no effect on basal PLD in GC cells, nor on 1alpha,25-(OH)(2)D(3)-dependent PKC. Inhibition of PI-PLC blocked the 1alpha,25-(OH)(2)D(3)-dependent increase in PKC activity but inhibition of PC-PLC had no effect. Activation of PLA(2) with melittin inhibited basal and 24R,25-(OH)(2)D(3)-stimulated PKC in RC cells and stimulated basal and 1alpha,25-(OH)(2)D(3)-stimulated PKC in GC cells, but wortmannin had no effect on the melittin-induced changes in either cell type. Pertussis toxin modestly increased the effect of 24R,25-(OH)(2)D(3) on PKC, whereas GDPbetaS had no effect, suggesting that PLD2 is the isoform responsible. This indicates that 1alpha,25-(OH)(2)D(3) regulates PKC in GC cells via PI-PLC and PLA(2), but not PC-PLC or PLD, whereas 24R,25-(OH)(2)D(3) regulates PKC in RC cells via PLD2.

GLYCOPHOSPHATIDYLINOSITOL-ANCHORED PROTEINS INPARAMECIUM TETRAURELIA

We have begun to characterize the glycophosphatidylinositol (GPI)-anchored proteins of the Paramecium tetraurelia cell body surface where receptors and binding sites for attractant stimuli are found. We demonstrate here (i) that inositol-specific exogenous phospholipase C (PLC) treatment of the cell body membranes (pellicles) removes proteins with GPI anchors, (ii)that, as in P. primaurelia, there is an endogenous lipase that responds differently to PLC inhibitors compared with its response to an exogenous PLC, (iii) that salt and ethanol treatment of cells removes GPI-anchored proteins from whole, intact cells, (iv) that Triton X-114 phase partitioning shows that many GPI-anchored proteins are cleaved from pellicles by the endogenous lipase and enter the aqueous phase, and (v) that integral membrane proteins are not among those cleaved with PLC or in the salt/ethanol wash.

Antisera against the proteins removed by the salt/ethanol washing procedure include antibodies against large surface antigens, which we confirm in this species to be GPI-anchored, and against an array of proteins of smaller molecular mass. These antisera specifically block the chemoresponse to some stimuli, such as folate, which we suggest are signaled through GPI-anchored receptors. Responses to cyclic AMP, which we believe involve an integral membrane protein receptor, and to NH4Cl, which requires no receptor, are not affected by the antisera. Antiserum against a mammalian GPI-anchored folate-binding protein recognizes a single band among the GPI-anchored salt and ethanol wash proteins. The same antiserum specifically blocks the chemoresponse to folate.

Regulation of phospholipase D (PLD) in growth plate chondrocytes by 24R,25-(OH)2D3 is dependent on cell maturation state (resting zone cells) and is specific to the PLD2 isoform

Many of the effects of 1alpha,25-(OH)2D3 and 24R,25-(OH)2D3 on costochondral chondrocytes are mediated by the protein kinase C (PKC) signal transduction pathway. 1alpha,25-(OH)2D3 activates PKC in costochondral growth zone chondrocytes through a specific membrane receptor (1alpha,25-mVDR), involving rapid increases in diacylglycerol via a phospholipase C (PLC)-dependent mechanism. 24R,25-(OH)2D3 activates PKC in resting zone chondrocytes. Although diacylglycerol is increased by 24R,25-(OH)2D3, PLC is not involved, suggesting a phospholipase D (PLD)-dependent mechanism. Here, we show that resting zone and growth zone cells express mRNAs for PLD1a, PLD1b, and PLD2. Both cell types have PLD activity, but levels are higher in resting zone cells. 24R,25-(OH)2D3, but not 24S,25-(OH)2D3 or 1alpha,25-(OH)2D3, stimulates PLD activity in resting zone cells within 3 min via nongenomic mechanisms. Neither 1alpha,25-(OH)2D3 nor 24R,25-(OH)2D3 affected PLD in growth zone cells. Basal and 24R,25-(OH)2D3-stimulated PLD were inhibited by the PLD inhibitors wortmannin and EDS. Inhibition of phosphatidylinositol 3-kinase (PI 3-kinase), PKC, phosphatidylinositol-specific PLC (PI-PLC), and phosphatidylcholine-specific PLC (PC-PLC) had no effect on PLD activity. Thus, 24R,25-(OH)2D3 stimulates PLD, and PI 3-kinase, PI-PLC and PKC are not involved, whereas PLD is required for stimulation of PKC by 24R,25-(OH)2D3. Pertussis toxin, GDPbetaS, and GTPgammaS had no effect on 24R,25-(OH)2D3-dependent PLD when added to cell cultures, indicating that G-proteins are not involved. These data show that PKC activation in resting zone cells is mediated by PLD and suggest that a functional 24R,25-(OH)2D3-mVDR is required. The results also support the conclusion that the 24R,25-(OH)2D3-responsive PLD is PLD2, since this PLD isoform is G-protein-independent.

Production of endothelin by cultured human endothelial cells following exposure to nicotine or caffeine

This study evaluated endothelin production by endothelial cells after exposure to nicotine or caffeine. Vasoconstrictive properties have been attributed to both nicotine and caffeine. The presence of endothelin, a potent vasoconstrictor itself, was determined using a radioimmunoassay. The optimal stimulatory doses for nicotine and caffeine were determined to be 1.0 micromol/L and 1.0 mmol/L, respectively. When endothelin production was evaluated over time after exposure to the optimal dose of each agent, it was determined that nicotine stimulated maximum endothelin production within 5 minutes. Caffeine failed to cause a distinct peak of endothelin production within 20 minutes. These results suggest that nicotine may have a possible acute and short-lived effect on the vasoconstrictive response associated with endothelin, while caffeine-induced endothelin release may require more long-term exposure.

Caffeine- and noradrenaline-induced contractions of human vas deferens: contrasting effects of procaine, ryanodine and W-7

1. The effects of ryanodine, procaine, and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) on noradrenaline (NA)- and caffeine-induced contractions of human vas deferens were investigated. 2. In the presence of nifedipine (1 microM), NA ( 100 microM) evoked biphasic contractions. Caffeine (20 mM) evoked repeatable tonic contractions. 3. Ryanodine (30 microM) inhibited the initial but not the secondary component of NA contractions. Procaine (1 and 10 mM) inhibited both components. Contractions induced by caffeine were unaffected by ryanodine or procaine. 4. The calmodulin antagonist W-7 (100 microM) reduced, in a reversible manner, both components of NA-induced response. Caffeine-induced contractions were also reduced in most preparations (8 of 11). In all preparations, contractions induced by caffeine were markedly inhibited after the washout of W-7. Higher doses of W-7 (300 microM) induced an increase in basal tension. 5. These results indicate that NA contracts the longitudinal muscle of human vas deferens by a ryanodine-sensitive calcium-induced calcium release (CICR) mechanism and, in addition, a ryanodine-insensitive pathway: both are sensitive to procaine. In contrast, contraction induced by caffeine is mediated by a pathway that is atypically insensitive to either ryanodine or procaine. The sensitivity of NA- and caffeine-induced contraction to W-7 suggests a role for calcium and its interaction with calmodulin in the response to both agents. The paradoxical action of W-7 is discussed.

Intracellular mechanisms of constriction of rat aorta by ethanol

The intracellular mechanisms mediating vasoconstriction by ethanol are poorly understood. This investigation was designed to provide evidence on the role of protein kinase C (PKC) and calmodulin in vasoconstriction by ethanol. We studied helically cut strips of rat aorta that were exposed to ethanol before and in the presence of the PKC inhibitors calphostin C (79, 239, and 798 nM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7, 10 microM), and the calmodulin inhibitor, trifluoperazine (TFP, 10 microM). To test for the specificity of the PKC inhibitors, we measured the responses of aortas to potassium and phorbol 12-myristate 13-acetate (PMA) in the absence and presence of calphostin C and H7. To test for the specificity of TFP, we measured the responses of aortas to serotonin, potassium, PMA, and the thromboxane A2 mimic. 9,11-dideoxy-11 alpha, 9 alpha-epoxy-methanoprostaglandin F2a (U46619), in the absence and presence of TFP. We also studied the effect of the combination of calphostin C and TFP on constriction of the aorta by ethanol. We also measured the importance of intracellular and extracellular calcium in constriction of the aorta by ethanol. Force generation was measured before, and then during exposure of the strips to calcium-free buffer with EGTA, or calcium-free buffer with EGTA plus caffeine. We found that both PKC inhibitors antagonized vasoconstriction by ethanol and PMA. However, H7 antagonized contractions by potassium, but calphostin C did not. We found that TFP caused 99 +/- 1% inhibition of maximum contraction to serotonin, 90 +/- 4% inhibition of maximum contraction to potassium, 63 +/- 6% inhibition of maximum contraction to PMA, and 8 +/- 5% inhibition of maximum contraction to U46619. TFP caused a 22 +/- 8% inhibition of contraction to ethanol. The combination of TFP and calphostin C antagonized vasoconstriction by ethanol to a degree similar to that of calphostin C alone. We also found that contractions to ethanol were only 16 +/- 7% of control values in a calcium-free plus EGTA buffer. Contractions to ethanol were 0 +/- 1% of control values in calcium-free buffer with EGTA plus caffeine. We conclude that: 1-vasoconstriction by ethanol is, at least in part, mediated by PKC; 2-constriction by ethanol is mediated to a minimal extent by calmodulin, and 3-part of the constriction by ethanol of the aorta is mediated by a caffeine-sensitive pool of intracellular calcium.

Identification of casoxin C, an ileum-contracting peptide derived from bovine kappa-casein, as an agonist for C3a receptors

Casoxin C (Tyr-Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg) is a bioactive peptide that was isolated from a tryptic digest of bovine kappa-casein as an anti-opioid peptide in longitudinal strips of guinea pig ileum. Casoxin C also evokes contraction of the ileal strips, and we found that this process was biphasic with rapid and slow components. The contractile profile was very similar to that of human complement C3a(70-77), which is the COOH-terminal octapeptide of C3a and has, although less potent, qualitatively the same biological activities as C3a. Casoxin C also has homology with C3a(70-77). The rapid contraction was mediated by histamine release and the slow contraction was mediated by a prostaglandin E2-like substance, judging from the effects of various pharmacological inhibitors and antagonists on the ileal contraction. Casoxin C had affinity for C3a receptors (IC50 = 40 microM) in the radioreceptor assay. In addition, casoxin C showed phagocyte-stimulating activities. Casoxin C is therefore the first milk-derived peptide identified, that acts through complement C3a receptors.

Possible involvement of endothelial leukotrienes in acetylcholine-induced contraction in rabbit coronary artery

In endothelium-intact preparations of rabbit coronary artery, acetylcholine (3 x 10(-8)-10(-6) M) caused a contraction in the presence of N omega-nitro-L-arginine methyl ester (10(-4) M). Removal of endothelium significantly attenuated the contraction. The present experiments were undertaken to elucidate whether the acetylcholine-induced contraction in endothelium-intact preparations was due to arachidonic acid metabolites, endothelin or superoxide. The acetylcholine-induced contraction in endothelium-intact preparations was attenuated by manoalide (10(-6) M and 3 x 10(-6) M) or oleyloxyethyl phosphorylcholine (10(-5) M) (phospholipase A2 inhibitors), BAY x 1005 (3 x 10(-6) and 10(-5) M) or L 663,536 (10(-6) and 10(-5) M) (leukotriene synthesis inhibitors) and ONO-1078 (10(-6) and 3 x 10(-6) M) or SK&F 104353 (10(-6) and 3 x 10(-6) M) (leukotriene antagonists). The contraction was not affected by aspirin (10(-4) M) or indomethacin (10(-6) M) (cyclooxygenase inhibitors), S-1452 (10(-8) M) or ONO-3708 (10(-7) M) (thromboxane A2 antagonists), FR139317 (10(-6) M) (endothelin receptor antagonist) or superoxide dismutase (150 u/ml) combined with catalase (1000 u/ml), or allopurinol (10(-5) M) (antioxidants). In contrast, the endothelium-independent contraction induced by acetylcholine was unaffected by any of these inhibitors and antagonists listed above. The present experiments demonstrate that in the presence of N omega-nitro-L-arginine methyl ester, acetylcholine partly causes an endothelium-dependent contraction in rabbit coronary artery which is probably due to leukotriene C4 and D4, but does not involve production of thromboxane A2, endothelin or superoxide.

Studies on the ileum-contracting mechanisms and identification as a complement C3a receptor agonist of oryzatensin, a bioactive peptide derived from rice albumin

Oryzatensin (Gly-Tyr-Pro-Met-Tyr-Pro-Leu-Pro-Arg) is an ileum-contracting and immunostimulating peptide derived from rice albumin. The mechanisms for the ileal contraction that it induces, consisting of rapid and slow components, were examined. The rapid contraction was mediated by histamine release and the slow contraction by a prostaglandin E2-like substance, judging from the effects of various pharmacological inhibitors and antagonists on ileal contraction and titration of histamine release. The contractile profile was very similar to that of human complement C3a(70-77), which is the COOH-terminal octapeptide of C3a and has, although less potent, qualitatively the same biological activities as C3a. Oryzatensin showed homology with C3a(70-77) and affinity for C3a receptors (IC50 = 44 microM) by radioreceptor assay. This is the first report of a food-derived bioactive peptide acting through complement C3a receptors.

Pharmacological natures of caffeine-induced endothelium-dependent and -independent contraction in canine mesenteric artery

The present experiments were carried out to elucidate whether pharmacological nature of caffeine (1 mM)-induced endothelium-dependent contraction (EDC) is different from that of caffeine (10 mM)-induced endothelium-independent contraction (EIC) in canine mesenteric artery. Caffeine (1 mM)-induced EDC was abolished when arterial strips were incubated in Ca(++)-free medium for 20 min, but EIC was not abolished. EGTA and EDTA (0.5 and 1 mM) attenuated the EDC, and at the concentration of 2.5 mM completely abolished the EDC. Nifedipine (10(-6) and 3 x 10(-6) M), diltiazem (10(-6) M) and verapamil (10(-6) M) did not affect the caffeine (1 mM)-induced EDC. Lemakalim (10(-8), 3 x 10(-8) and 10(-7) M) attenuated the caffeine (1 mM)-induced EDC in a concentration-dependent manner. Lemakalim (10(-7) M) nearly abolished the EDC. The inhibitory effect of lemakalim (10(-7) M) on the EDC was antagonized in the presence of glibenclamide (3 x 10(-6) M). In contrast, caffeine (10 mM)-induced EIC was resistant to lemakalim at higher concentration (3 x 10(-7) M). Forskolin (10(-7), 3 x 10(-7) and 10(-6) M) significantly attenuated both the caffeine (1 mM)-induced EDC and caffeine (10 mM)-induced EIC. The inhibitory effect of forskolin on the EDC was augmented in the presence of rolipram (10(-6) M). Nitroglycerin (10(-5) M) attenuated significantly caffeine-induced both EDC and EIC. The inhibitory effect of nitroglycerin on the EDC was augmented in the presence of zaprinast (10(-5) M). The present experiments demonstrate that caffeine-induced EDC is due to nifedipine-resistant and lemakalim-sensitive Ca++ mobilization and the EIC is due to both nifedipine- and lemakalim-resistant Ca++ mobilization in canine mesenteric artery.