Cytosolic calcium regulates phorbol diester binding affinity in intact phagocytes

Regulation of L-type Voltage Gated Calcium Channel CACNA1S in Macrophages upon Mycobacterium tuberculosis Infection

We demonstrated earlier the inhibitory role played by Voltage Gated Calcium Channels (VGCCs) in regulating Mycobacterium tuberculosis (M. tb) survival and pathogenesis. In this report, we investigated mechanisms and key players that regulate the surface expression of VGCC-CACNA1S by Rv2463 and M. tb infection in macrophages. Our earlier work identified Rv2463 to be expressed at early times post infection in macrophages that induced suppressor responses to dendritic cells and macrophages. Our results in this study demonstrate a role of MyD88 independent TLR pathway in mediating CACNA1S expression. Dissecting the role for second messengers, we show that calcium homeostasis plays a key role in CACNA1S expression during M. tb infection. Using siRNAs against molecular sensors of calcium regulation, we show an involvement of ER associated Stromal Interaction Molecules 1 and 2 (STIM1 and STIM2), and transcription factor pCREB, towards CACNA1S expression that also involved the MyD88 independent pathway. Interestingly, reactive oxygen species played a negative role in M. tb mediated CACNA1S expression. Further, a cross-regulation of ROS and pCREB was noted that governed CACNA1S expression. Characterizing the mechanisms governing CACNA1S expression would improve our understanding of the regulation of VGCC expression and its role in M. tb pathogenesis during M. tb infection.

The involvement of protein kinases in signalling of opioid agonist FK 33-824 in porcine granulosa cells

It is known that acute action of mu opioid receptor agonist, FK 33-824, results in an inhibition of oestradiol (E2) secretion by porcine granulosa cells from large follicles, but the opioid mode of action is unknown. In the present study, the involvement of two signal transduction pathways, phospholipase C/protein kinase C and adenylyl cyclase/protein kinase A, in mechanism of the opioid action was investigated. Treatment of pig granulosa cells with FK 33-824 at the dose 1 nM suppressed E2 secretion. Protein kinase C (PKC) inhibitors - staurosporine (1-100 nM), d-sphingosine (10-500 nM) and PKCi (100-2000 nM) - both alone and in combination with FK 33-824 reduced E2 release from the cells in relation to the control group. The inhibitory effect of the opioid on E2 output was also observed in PKC-deficient granulosa cells. PKC activator, PMA (10 and 100 nM) significantly attenuated the inhibitory effect of the opioid agonist. FK 33-824 also inhibited 3[H]phorbol 12,13 dibutyrate (3[H]PDBu) specific binding by granulosa cells. Adenylyl cyclase (AC) engagement in opioid signal transduction was assayed after 2-h and 4-h incubations of granulosa cells. During 2-h incubation, FK 33-824 at the dose 1 nM decreased cAMP secretion. Prolongation of the incubation up to 4 h caused disappearance of the opioid action. The addition of protein kinase A (PKC) inhibitor, PKAi (100-2000 nM), alone or together with FK 33-824, was followed by an inhibition of E2 secretion. FK 33-824 with the highest dose of PKAi (2000 nM) significantly inhibited E2 secretion by the cells in comparison to these agents tested separately. The opioid added in combination with PKA activator, 8BrcAMP (1000 microM), caused attenuation of stimulatory effect of 8BrcAMP. Collectively, these results suggest that acute action of mu opioid agonist on porcine granulosa cells leads to decrease of enzymatic activity of PKC and AC/PKA. It is not ruled out that other signal transduction pathways - not considered in this study - may also be engaged in the opioid mechanism of action in these cells.

Prolactin signalling in porcine theca cells: the involvement of protein kinases and phosphatases

The hypothesis that protein kinase C (PKC) and tyrosine kinases, as well as serine-threonine and tyrosine phosphatases, are involved in prolactin (PRL) signalling in theca cells harvested from porcine follicles was tested. Theca cells were incubated with PRL for 24 h to stimulate progesterone (P4) production. In addition, treatments included inhibitors of PKC and tyrosine kinases, as well as serine-threonine phosphatase inhibitor and tyrosine phosphatase inhibitor. Prolactin significantly stimulated P4 production by theca cells and all inhibitors suppressed the PRL-stimulated P4 production. After incubation with PRL for 2, 5, 10 or 20 min, theca cells were homogenized and cytosolic and membrane fractions were obtained. This was followed by determination of PKC activity in partially purified subcellular fractions by measuring the transfer of 32P from [gamma-32P] adenosine triphosphatase (ATP) to histone III-S. In unstimulated porcine theca cells the major proportion of PKC activity was present in the cytosol. Incubation of cells with PRL resulted in a rapid, time-dependent increase in the amount of PKC activity in the membrane fraction. Protein kinase C activity in the membrane fraction was maximal after 10 min of cells' exposure to PRL. Protein kinase C activation was assessed also by measuring the specific association of 3H-phorbol dibutyrate (3H-PDBu) with theca cells after treatment with PRL. Prolactin significantly increased 3H-PDBu-specific binding in theca cells. In contrast to PKC, total inositol phosphate accumulation was not affected by PRL in the current study. In summary, PRL stimulated P4 production by porcine theca cells derived from large follicles. The results of the study were consistent with the hypothesis that PKC is one of the intracellular mediators of PRL action in porcine theca cells. Protein kinase C activation does not appear to occur through the action of phosphatidylinositol-dependent phospholipase C. Moreover, the involvement of tyrosine kinases, as well as tyrosine and serine-threonine phosphatases, in PRL signalling in the examined cells is suggested.

The response of phospholipase C/protein kinase C and adenylyl cyclase/protein kinase A pathways in porcine theca interna cells to opioid agonist FK 33-824

Opioids were found as factors affecting porcine ovarian steroidogenesis. The mechanism of opioid action, however, on porcine theca interna cells is completely unknown. Therefore, the present study was designed to investigate the possible involvement of two intracellular pathways, phospholipase C/protein kinase C and adenylyl cyclase/protein kinase A, in opioid signal transduction in porcine theca cells treated with mu opioid receptor agonist, FK 33-824. Incubation of the cells for 4 h with FK 33-824 at the dose 1 nM resulted in decreases in inositol phosphate accumulation as well as androstenedione (A(4)), testosterone (T), and estradiol (E(2)) secretions. Protein kinase C (PKC) inhibitors, staurosporine (1-100 nM), D-sphingosine (10-500 nM), and PKCi (100-2000 nM), both added alone and together with the opioid agonist, depressed release of the steroid hormones. PKC activator, phorbol ester (PMA, 1-100 nM), used alone was without effect on theca cell steroidogenesis, but added in combination with FK 33-824 abolished inhibitory influence of the opioid on A(4), T, and E(2) output. The steroid hormone secretion by PKC-deficient theca cells was inhibited by the opioid agonist. FK 33-824 also suppressed PKC activity reducing [(3)H]PDBu specific binding to theca cells, whereas ionomycin (a positive control) increased labeled phorbol ester binding to the cells. In the next experiment, cAMP release from theca cells during 2 and 4 h incubations with FK 33-824 (1-100 nM), naloxone (10 microM; opioid receptor antagonist), and LH (100 ng/mL; a positive control) was examined. FK 33-824 at the dose 1 nM inhibited cAMP secretion during 2 h incubation, but had no effect during longer incubation. LH in a manner independent on incubation time multiplied cAMP release. Protein kinase A inhibitor, PKAi (100-2000 nM), alone and in combination with FK 33-824 (1 nM), inhibited A(4), T, and E(2) secretions by theca cells. PKA activator, 8BrcAMP (10-1000 microM), stimulated the steroid hormone release, but this stimulatory effect was diminished in the presence of FK 33-824. The results allow to suggest that opioid peptides affect porcine theca cell steroidogenesis and their acute action on the cells is connected with the inhibition of phospholipase C/protein kinase C and adenylyl cyclase/protein kinase A signal transduction systems.

Prolactin signaling in porcine adrenocortical cells: involvement of protein kinases

Prolactin (PRL) was found to have a stimulatory effect on adrenal steroidogenesis in vivo and in vitro in several species including pigs. PRL signal transduction pathways, however, in adrenocortical cells are poorly recognized. Therefore, the goal of this paper is to ascertain the involvement of protein kinase C (PKC) and tyrosine kinases in PRL signaling in porcine adrenal cortex. Adrenals were harvested from locally slaughtered mature gilts. Cortical cells were dispersed by sequential treatment with collagenase. The cells were seeded into 24-well culture plates at a density of 3 x 10(5)/mL. Cells were incubated with or without PRL (500 ng/mL), ACTH (5 nM--a positive control), tyrosine kinase inhibitor--genistein (1; 2.5 or 5 microM), PKC inhibitor--sphingosine (20-1000 nM) and PKC activators--diacylglycerol (DiC8; 10-100 microM) and phorbol ester (PMA; 1-1000 nM). All incubations were performed for 8 h (95% air and 5% CO(2), 37 degrees C). PRL and ACTH (P < 0.05) increased cortisol and androstenedione (A(4)) secretion. DiC8 and PMA mimicked the stimulatory effect of PRL. Sphingosine (P < 0.05) suppressed basal and PRL-stimulated steroid secretion. Genistein inhibited (P < 0.05) PRL-stimulated cortisol secretion and enhanced (P < 0.05) basal and PRL-stimulated A(4) secretion. Moreover, PKC activation was assessed by measuring the specific association of [3H]phorbol dibutyrate ([3H]PDBu) with adrenocortical cells after treatment with PRL or ionomycin (a positive control). PRL (within 2-3 min) and ionomycin (within 2-5 min) increased (P < 0.05) specific binding of [3H]PDBu to the porcine adrenocortical cells. In addition, PRL did not augment the cortisol and A(4) secretion by PKC-deficient adrenocortical cells. In conclusion, presented results support the hypothesis that PKC and tyrosine kinases are involved in PRL signaling in adrenocortical cells in pigs. Moreover, activation of PKC is associated with the increased secretion of cortisol and A(4).

Studies of the cellular mechanisms underlying the vasorelaxant effects of rutaecarpine, a bioactive component extracted from an herbal drug

We conducted studies to investigate the nature and underlying mechanisms of the vascular effects of rutaecarpine (Rut), an alkaloid isolated from the Chinese herbal drug Evodia rutaecarpa. By using largely the effects on phenylephrine (PE)-induced contraction in the isolated rat aorta as the experimental index and by comparison with several known vascular muscle relaxants such as acetylcholine (ACh), histamine, and A23187, Rut relaxed PE-precontracted aorta in concentration-(10(-7)-10(-4) M) and endothelium-dependent manners. Studies with appropriate antagonists indicated that this was coupled to nitric oxide (NO) and guanylyl cyclase. Extracellular Ca2+ removal and treatment with the intracellular Ca2+ antagonist, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), suggested that influx of extracellular Ca2+ was the major factor contributing to the action of Rut. Pertussis toxin suppressed the relaxation potency of histamine but had no effects on the actions of Rut. NaF, the G proteins activator, attenuated the actions of ACh, but only minimally affected Na-NP, A23187, and Rut. 1-[6-{[17 beta-3-methoxyestra-1,2,3(10)-trien-17-yl]amino} hexyl]-1H-pyrrole-2,5-dione (U73122), the phospholipase C inhibitor, again suppressed the actions of ACh but had few effects on A23187 and Rut. Taken together, these results suggest that these vasorelaxants had different cellular mechanisms and that neither pertussis toxin-sensitive Gi protein, other G proteins, nor phospholipase C activation was involved in the cellular response to rutaecarpine.

High concentrations of cholecystokinin octapeptide suppress protein kinase C activity in guinea pig pancreatic acini

In pancreatic acini, calcium-mobilizing agents increase intracellular calcium and stimulate the production of diacylglycerol, and then activate protein kinase C (PKC). However, there are few studies which have examined the activation of PKC in intact acini. To examine the activation of PKC in intact acini by calcium-mobilizing agents, we measured the binding of [3H]phorbol-12,13-dibutyrate (PDBu) to intact acini. Acini were incubated with 10 nM [3H]PDBu at 25 degrees C with or without agents. The binding reactions were terminated by filtration. The filters were counted by a scintillation counter after washing. Acini possessed a single class of binding sites to PDBu, with Kd = 70 nM. CCK-8 and carbachol upregulated the binding affinity of PKC to PDBu in the acini. The ability of calcium-mobilizing agents to increase binding of [3H]PDBu to the acini had a close correlation to their ability to stimulate the amylase secretion from the acini, and higher concentrations of CCK-8 for amylase secretion suppressed binding of [3H]PDBu to the acini. 8Br-cAMP, 8Br-cGMP, and calcium ionophore did not inhibit the maximal activation of PKC induced by CCK-8. The calmodulin inhibitor W7 did not reverse the inhibitory effect of higher concentrations of CCK-8 on PKC activation. These results indicate that calcium-mobilizing agents upregulate the binding affinity of PKC to PDBu in intact acini, and that higher concentrations of CCK-8 for amylase secretion may activate the intracellular mechanism that inhibits PKC activity in acini. This inhibitory mechanism was mediated by some other mechanism other than cAMP-, cGMP-, calcium- and calmodulin-dependent mechanisms.

Arachidonic acid inhibits hCG-stimulated progesterone production by corpora lutea of primates: potential mechanism of action

Arachidonic acid (AA) is a precursor of metabolites known to affect the corpus luteum (CL) in many species, including primates. We have shown that some of these products (prostaglandins F2 alpha and E2) inhibit pro-gesterone (P4) production and activate the phosphatidylinositol (PI) pathway in CL of rhesus monkeys. A direct role of AA in luteal function has also been suggested. The current experiments were designed to investigate the effect of AA on P4 synthesis and to examine the ability of AA to activate the PI pathway in CL of rhesus monkeys. Basal and hCG-stimulated P4 production by luteal cells collected during the midluteal phase was measured after treatment with AA (1, 5, and 10 microM) or linoleic acid (1, 5, and 10 microM). Dispersed cells (50,000/tube) were incubated at 37 degrees C for 2 h. AA elicited a dose-dependent decrease in hCG-stimulated, but not in basal, P4 production. hCG-stimulated P4 production was reduced (P < 0.01) at AA doses of 5 microM (12.1 +/- 1.5 ng/mL) and 10 microM (8.6 +/- 1.8 mg/mL) to hCG alone (18 +/- 1.6 ng/mL). There was no significant effect of 1 microM AA (15.2 +/- 1.6). Response to linoleic acid was dissimilar and was not dose-dependent. Viability of cells was not affected by any treatment. Indomethacin, a prostaglandin synthesis inhibitor, and nordihydroguaiaretic acid, an inhibitor of lipoxygenase, did not interfere with the inhibitory effect of AA. Activation of the PI pathway was assessed by monitoring the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PIP2) to inositol phosphates and by monitoring increases in intracellular free calcium concentrations ([Ca2+]i) in individual cells. Moreover, the ability of AA to activate protein kinase C (PKC) in luteal cells was measured using a [3H]phorbol dibutyrate (PDBu) binding assay. AA did not alter PIP2 hydrolysis or [Ca2+]i, however, AA (10 microM) increased specific binding of [3H]PDBu to luteal cells (P < 0.05). We conclude that AA inhibits hCG-stimulated P4 production by primate luteal cells. AA exerts this action without being converted to prostaglandins or leukotrienes. This inhibition may be mediated through the activation of PKC. These results suggest a possible role for AA in the regulation of luteal function in primates, and that PKC-activation by AA may promote its effects.

Regulation of endothelial adhesion molecules by ligands binding to the scavenger receptor

Monocyte adherence to the endothelium, their penetration to the subendothelial space and excessive lipid accumulation (foam cell formation) are the initial events in atherogenesis. Scavenger receptors have been reported to play an important role in foam cell formation, since modified low density lipoproteins can be taken up via scavenger receptors in a non-down-regulated fashion. In this study we demonstrate that stimulation of scavenger receptors in endothelial cells induces the expression of endothelial adhesion molecules. Polyinosinic acid (poly I), a known scavenger receptor ligand, significantly induced the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on human umbilical vein endothelial cells when compared with polycytidylic acid (poly C), a structurally related compound to poly I, which does not bind to the scavenger receptor. The effect of scavenger receptor ligands on the endothelial cell line EA hy. 926 was also tested. Poly I up-regulated ICAM-1 expression also on EA hy. 926 cells, while it had no effect on IL-1 beta or tumour necrosis factor-alpha (TNF-alpha) production on the same cell line. Poly I-induced ICAM-1 expression on EA hy. 926 cells could be inhibited by H7, a protein kinase C inhibitor, while HA 1004, a preferential protein kinase A inhibitor, had no effect on ICAM-1 expression. The role of protein kinase C in scavenger receptor-mediated adhesion molecule upregulation was confirmed by the ability of poly I to directly activate protein kinase C, when measured with 3H-phorbol dibutyrate binding to EA hy. 926 cells, while poly C again was ineffective.

Signal transduction mechanisms of HLA-DR-mediated interleukin-1 beta production in human monocytes. Role of protein kinase C and tyrosine kinase activation

The signal transduction pathways leading to the expression of IL-1 beta in human monocytes via HLA-DR stimulation were investigated. SEB, a staphylococcal enterotoxin that binds to HLA-DR molecules, induced IL-1 beta expression in human monocytes. Protein synthesis inhibition by cycloheximide did not inhibit SEB-mediated IL-1 beta signal, indicating that protein synthesis is not required for the MHC class-II-mediated IL-1 beta expression. The effect of PKC, PKA, and tyrosine kinase inhibitors on HLA-DR-mediated IL-1 beta mRNA expression was then determined. H7, a preferential PKC inhibitor, completely inhibited IL-1 beta signal induced by SEB. The role of PKC on HLA-DR-mediated IL-1 beta induction was further confirmed by the ability of SEB to activate PKC on monocytes directly when measured with labeled phorbol ester ([3H]Pbt2)-binding capacity of whole cells. HA 1004, a preferential PKA inhibitor, and isobutyl-methyl-xanthine (IBMX), which inhibits the degradation of cAMP, had no effect on SEB-induced IL-1 beta signal, excluding the role of cAMP on HLA-DR-mediated IL-1 beta expression. Two tyrosine kinase inhibitors, genistein and dihydroxycinnamate, both inhibited SEB-induced IL-1 beta mRNA in monocytes. SEB also induced enhanced tyrosine phosphorylation of several proteins in human monocytes when determined with antiphosphotyrosine immunoblotting. Our results demonstrate that both PKC and protein tyrosine kinases are involved in HLA-DR-induced IL-1 beta expression in human monocytes.

Glutamate stimulates [3H]phorbol 12,13-dibutyrate binding in cultured Bergmann glia cells

The effect of L-glutamate and its structural analog kainate on the binding of [3H]phorbol 12,13-dibutyrate was examined in cultured chick cerebellar Bergmann glia cells. Both glutamate and kainate evoke a dose-dependent increase in the maximal number of binding sites for [3H]phorbol 12,13-dibutyrate in intact cells reflecting an activation and translocation of the Ca2+/diacylglycerol-dependent protein kinase (protein kinase C, PKC) from cytosol to the plasma membrane. Glutamate and kainate responses were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) indicating that the increase in [3H]phorbol 12,13-dibutyrate binding sites is mediated by an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor. Since Bergmann glia AMPA/kainate receptors are probably mediators of the efficacy of the parallel fiber-Purkinje cell synapse, the present findings suggest that the Ca2+/PKC signalling cascade might play a role in such modulation.

Receptors for tumor-promoting phorbol esters in rat ventral prostate

The presence of tumor-promoting phorbol ester receptors in rat prostate was investigated by studying the binding of phorbol diester 12,13-dibutyrate (PDBu) in both soluble and particulate subcellular fractions. Binding of [3H]PDBu to the soluble fraction was optimal after the addition of phosphatidylserine (0.1 mg/ml) and Ca2+ (1 mM). Both subcellular fractions exhibited a single class of PDBu receptor (Kd between 97 and 128 nM) as shown by saturation binding experiments. Phorbol esters with tumor-promoting activity showed a higher affinity for these receptors than did endogenous ligands such as diacylglycerols whereas phorbol esters without tumor-promoting activity were ineffective even at concentrations as high as 1 microM. These properties are highly representative of protein kinase C activity.

Role of protein kinase C in bradykinin-induced prostaglandin formation in osteoblasts

Bradykinin (1 microM, 5 min) induced translocation of protein kinase C (PKC) to the plasma membrane fraction in osteoblastic MC3T3-E1 cells. Bradykinin also enhanced the binding of phorbol 12,13-dibutyrate (PDBu) to intact cells, a measure of PKC activation. Addition of bradykinin (1 microM) to cells preincubated with [3H]PDBu (10 nM, 20 min) caused an increase in specific PDBu binding that was maximal after 5-10 min. The bradykinin-induced enhancement of PDBu binding was seen at 1 nM and was maximal at 10 nM. The bradykinin B1 receptor agonist des-Arg9-bradykinin (1 microM) did not enhance specific PDBu binding to intact MC3T3-E1 cells. PDBu at and above 3 nM stimulated the formation of prostaglandin E2 (PGE2) in MC3T3-EI cells. This stimulatory effect was seen after 15-20 min incubation. The Ca2+ ionophore A23187 at and above 1 microM induced a rapid (within seconds) burst of PGE2 formation in MC3T3-E1 cells. The effect of PDBu and A23187 on PGE2 formation was synergistic. The PKC inhibitor staurosporine (200 nM) inhibited basal as well as bradykinin-induced prostaglandin-formation in MC3T3-E1 cells.

IN CONCLUSION

bradykinin enhances PKC activation in osteoblastic MC3T3-E1 cells. This kinase activation may be involved in bradykinin-induced prostaglandin formation.

Drugs acting on the intracellular signalling system

Cellular response to extracellular messages is a basic process to maintain and to support cell life. Several signalling molecules important as sites of therapeutic drug action are involved in the response. Recent studies on life sciences have elucidated molecular properties of intracellular signalling factors and mechanisms of cascading. Novel drugs acting on signalling molecules and possessing new sites and mechanisms of action have been found. This article summarizes the properties (subtypes, structures, functions) of signalling factors (receptors, ion channels, GTP binding proteins, second messenger-generating enzymes, second messenger-metabolizing enzymes, second messengers protein kinases, protein phosphatases) and lists in Tables A-H drugs that act on signalling molecules and which should find clinical use.

Direct assay of membrane-associated protein kinase C activity in B lymphocytes in the presence of Brij 58

This paper describes a simple and direct procedure for assaying Ca(2+)-dependent protein kinase C (PKC) activity in membrane fractions isolated from purified murine B lymphocytes (B cells) treated with phorbol 12-myristate 13-acetate (PMA). The results indicate that membrane-bound PKC in B cells, treated with PMA, can be measured directly in the presence of 0.5% Brij 58 by assaying the transfer of 32P from [gamma-32P]ATP to histone type III-S. This method obviates the need for partial purification of the protein kinase by ion-exchange chromatography prior to assaying PKC activity. The properties of membrane-associated PKC activity in B cells have been characterized, and the kinetics of PMA-induced translocation of PKC in cultured murine B cells, the rat glial tumor clone C6, and primary neonatal osteoblastic cells have been defined by this direct assay. The results obtained with B cells and the other cell lines indicate that this direct assay procedure could be useful for studies on the factors controlling PKC translocation in a variety of cultured mammalian cells.

Alteration of cytoplasmic Ca2+ in resting and stimulated human neutrophils by short-chain carboxylic acids at neutral pH

The results reported here indicate that the short-chain carboxylic acids acetate and propionate stimulate cytoplasmic calcium mobilization in human polymorphonuclear leukocytes, while butyrate and lactate do not. Together with the results of previous work, this indicates that there are at least three classes of short-chain carboxylic acids: those which can alter only cytoplasmic pH (e.g., lactic acid), those which can alter cytoplasmic pH and actin (e.g., butyric acid), and those which can alter cytoplasmic pH, actin, and calcium (e.g., acetate and propionate).

Regulation of prostacyclin production by [Ca2+]i and protein kinase C in aortic smooth muscle cells

The respective roles of protein kinase C (PKC) and of cytosolic free Ca2+ concentration ([Ca2+]i) in prostacyclin synthesis were investigated in aortic smooth muscle cells by using A23187 and phorbol 12-myristate 13-acetate (PMA) to bypass the hormonal receptor. Exposure of the cells to A23187 markedly increased prostacyclin production, which was not affected by the PKC inhibitor staurosporine or by PKC depletion after prolonged incubation (48 h) of cells with PMA. The increase in [Ca2+]i induced by A23187 did not affect membranous or cytosolic PKC activity in control and PMA-stimulated cells. Activation of PKC by PMA, a weak stimulant of prostacyclin production by itself, strongly potentiated A23187-induced prostacyclin production, as well as that induced by the calcium-mobilizing hormone arginine vasopressin (AVP). The potentiating effect persisted for 30 min after the removal of PMA. However, this "memory" effect was not due to sustained levels of membranous PKC activity but probably to the prolonged influence of PKC-induced phosphorylation(s). Taken together, our results suggest that, although an increase in [Ca2+]i is sufficient for inducing prostacyclin production in rat aortic smooth muscle cells, activation of PKC is necessary for AVP-induced prostacyclin production in this same tissue.

Effect of Ca2+ modulators on acetylcholine-induced phasic and tonic contractions and A23187-induced contractions in ileal longitudinal muscle and IP3 production

The influence of different sources of Ca2+ on the Emax and ED50 values of acetylcholine (ACh)-induced phasic and tonic contractions and on A23187-induced contractions was studied using different extracellular Ca2+ concentrations ([Ca2+]o) and the Ca2+ modulators TMB-8 and D600. IP3 production induced by both stimulants was also studied. The results are compatible with: (a) the mobilization of Ca2+ from an intracellular source as a primary event in the phasic response. (b) The primary involvement of a D600-sensitive inward Ca2+ current in the ACh-tonic response. (c) An inward D600-sensitive Ca2+ current associated with the ionophore transported ion. (d) The involvement of an IP3 independent, TMB-8 sensitive mechanism of Ca2+ mobilization involved in the A23187-induced responses.

Polyamines enhance calcium mobilization in fMet-Leu-Phe-stimulated phagocytes

Spermidine and putrescine (50 microM-1 mM), found in exudates from infection sites, significantly enhance fMet-Leu-Phe-induced Ca2+ mobilization in differentiated HL-60 cells and polymorphonuclear leukocytes (PMNs) by delaying the return to basal cytosolic Ca2+ levels. This enhancement by polyamines is associated with inhibition of Ca2+ efflux across the plasma membrane. In parallel with their effects on Ca2+ signaling, polyamines also significantly prolong the kinetics of fMet-Leu-Phe-induced protein kinase C translocation. Thus, polyamines may play a novel role in modulating regulatory events in phagocytes.

Dopamine stimulates [3H]phorbol 12,13-dibutyrate binding in cultured striatal cells

The effect of dopamine (DA) on the binding of [3H]phorbol 12,13-dibutyrate ([3H]PdBu) in cultured rat striatal cells was examined. DA maximally increased specific [3H]PdBu binding by 70 +/- 10%, an increase comparable to that observed with norepinephrine (NE). This finding suggests that DA activates protein kinase C in cultured striatal cells, because increases in [3H]PdBu binding reflect translocation of protein kinase C. Half-maximal stimulation was observed with 10(-6) M DA. The peak response was observed at 2-3 min after addition of 10(-4) M DA, but [3H]PdBu binding was still increased above basal at 30 min. DA was not acting via an adrenergic receptor. Prazosin (10(-6) M) blocked the response to NE, suggesting mediation by an alpha 1-adrenergic receptor, but had little effect on the response to DA. Conversely, the D1 receptor antagonist SCH-23390 (10(-6) M) blocked the response to DA, but only partially inhibited the response to NE. Morphine (10(-6) M) inhibited the response to DA by 46 +/- 14%, but did not affect significantly the response to NE. The DA effect on [3H]PdBu binding is apparently independent of the increase in cyclic AMP seen on D1 receptor activation. Forskolin, apomorphine, and the D1 agonist SKF-38393 all increased cyclic AMP in striatal cells, but were less effective than DA in stimulating [3H]PdBu binding. The D2 agonist quinpirole was ineffective in stimulating either cyclic AMP or [3H]PdBu binding.

Proteinkinase C beta-isoform triggers the formation of prostanoids and superoxide in liver macrophages

The zymosan- and phorbolester-induced formation of prostanoids in cultured rat liver macrophages has been shown recently to be controlled by proteinkinase C (1). Using specific antibodies raised against the alpha-, beta-, gamma- and epsilon-isoforms of proteinkinase C, we show that proteinkinase-beta is the predominant isoform in rat liver macrophages. Northern blot analysis with a beta-isoform-specific c-DNA probe revealed the expression of m-RNA for proteinkinase-beta. In resting cells the beta-isoform of proteinkinase C is nearly equally distributed between the cytosolic and membrane fractions. Zymosan and phorbolester led to a translocation of proteinkinase-beta from the cytosol to the membranes, whereas exogenously added arachidonic acid and the calcium ionophore A23187 had no effect. These data indicate that the beta-isoform of proteinkinase C takes part in the prostaglandin and superoxide formation following PMA and zymosan treatment of rat liver macrophages.

Endothelin-1 in human skin: immunolocalization, receptor binding, mRNA expression, and effects on cutaneous microvascular endothelial cells

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, has been implicated in the maintenance of systemic and peripheral vascular tone. We have therefore sought direct evidence of a role for ET-1 in the regulation of blood flow and vascular tone in the human cutaneous microvasculature. Immunostaining for ET-1 was observed in all cutaneous blood vessels of normal human skin including the capillaries of the dermal papillae. Autoradiography showed specific binding of 125I-ET-1 over capillaries and larger blood vessels as well as hair follicles and sweat glands. In situ hybridization with a 32P-labeled RNA probe for ET-1 demonstrated mRNA for ET-1 in cultured human dermal microvascular endothelial cells (HDMEC). In HDMEC, basal release of PGE2 was significantly attenuated by ET-1 (100 pM-100 nM) (p less than 0.05, n = 7) with maximum inhibition in cells incubated with 10 nM ET-1. ET-1 also increased intracellular cAMP in a dose-dependent manner with a significant increase in HDMEC incubated with 100 nM ET-1 (p less than 0.05, n = 4). In HDMEC incubated with 100 nM ET-1, inhibition of PGE2 release was unaffected by the dihydropyridine Ca++ channel antagonist nifedipine or the extracellular Ca++ chelator EGTA, whereas the intracellular Ca++ chelator TMB-8 partially blocked the action of ET-1. In contrast, cAMP accumulation was significantly attenuated by EGTA (p less than 0.05, n = 4), nifedipine (p less than 0.05, n = 4), and TMB-8 (p less than 0.05, n = 4), indicating that the endothelial cell responses to ET-1 are complex and appear to involve both Ca(++)-sensitive and -insensitive pathways. These results provide evidence of an autocrine/paracrine role for ET-1 in the human cutaneous microvasculature.

Kinetics of phosphorylation of Na+/K(+)-ATPase by protein kinase C

The kinetics of phosphorylation of an integral membrane enzyme, Na+/K(+)-ATPase, by calcium- and phospholipid-dependent protein kinase C (PKC) were characterized in vitro. The phosphorylation by PKC occurred on the catalytic alpha-subunit of Na+/K(+)-ATPase in preparations of purified enzyme from dog kidney and duck salt-gland and in preparations of duck salt-gland microsomes. The phosphorylation required calcium (Ka approximately 1.0 microM) and was stimulated by tumor-promoting phorbol ester (12-O-tetradecanoylphorbol 13-acetate) in the presence of a low concentration of calcium (0.1 microM). PKC phosphorylation of Na+/K(+)-ATPase was rapid and plateaued within 30 min. The apparent Km of PKC for Na+/K(+)-ATPase as a substrate was 0.5 microM for dog kidney enzyme and 0.3 microM for duck salt-gland enzyme. Apparent substrate inhibition of PKC activity was observed at concentrations of purified salt-gland Na+/K(+)-ATPase greater than 1.0 microM. Phosphorylation of purified kidney and salt-gland Na+/K+ ATPases occurred at both serine and threonine residues. The 32P-phosphopeptide pattern on 15% sodium dodecyl sulfate-polyacrylamide gel electrophoresis after hydroxylamine cleavage of pure 32P-phosphorylated alpha subunit was the same for the two sources of enzyme, which suggests that the phosphorylation sites are similar. The results indicate that Na+/K(+)-ATPase may serve as a substrate for PKC phosphorylation in intact cells and that the Na+/K(+)-ATPase could be a useful in vitro model substrate for PKC interaction with integral membrane proteins.

Platelet protein phosphorylation and protein kinase C activation by phorbol esters with different biological activity and a novel synergistic response with Ca2+ ionophore

Phorbol esters with different biological activities have been tested for their ability to induce the phosphorylation of human platelet proteins. We have shown that only the potent platelet aggregatory phorbol esters were able to stimulate the phosphorylation of proteins of 76, 68, 47, 30 and 20 kDa in intact platelets. The ability of these esters to stimulate phosphorylation of the 47-kDa protein ('p47') correlated with their ability to cause platelet aggregation. When a non-platelet aggregatory deoxyphorbol (12-deoxyphorbol 13-phenylacetate 20-acetate) was combined with a subthreshold dose of the Ca2+ ionophore, A23187, a large increase in phosphorylation of p47 and a fourfold decrease in Ka was observed. This was in contrast to a barely detectable stimulation of phosphorylation at micromolar levels of this phorbol ester in the absence of the ionophore. This synergism was not evident for the potent platelet aggregatory derivatives. The Ka for DOPPA with a mixture of total platelet protein kinase C was 530 nM in the absence of calcium decreasing to 120 nM in the presence of calcium. In the presence of calcium, 12-deoxyphorbol 13-phenylacetate 20-acetate was shown to stimulate preferentially one of the isoforms of protein kinase C.

Protein phosphorylation associated with the stimulation of neutrophils. Modulation of superoxide production by protein kinase C and calcium

Neutrophils and other phagocytic cells of the immune system possess a superoxide-generating oxidase system which is essential for the efficient killing of microbes. The system is activated by a wide variety of stimuli, some of which operate through pathways involving protein kinase C (PKC), while others appear not to. The PKC-dependent pathway is probably the major signal transduction route for most of the stimuli. Alterations in cellular Ca2+ and diglyceride levels can have a pronounced stimulatory effect on this pathway by their ability to synergistically activate PKC. This review discusses PKC, the different interactions of this kinase with the plasmalemma that are important in superoxide production, the synergy between Ca2+ and diglyceride, and the nature of the phosphoproteins involved. Evidence supporting the existence of the PKC-independent pathway is also reviewed.

Intracellular Ca2+ potentiates Na+/H+ exchange and cell differentiation induced by phorbol ester in U937 cells

The human cell line U937 differentiates to monocyte macrophage-like cells in response to tumour-promoting phorbol esters. This effect is attributed to activation of protein kinase C. We show here that U937 cell differentiation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) is associated with cytoplasmic alkalinization. Ethyl-isopropyl-amiloride (EIPA), a potent inhibitor of Na+/H+ exchange, blocked both cytoplasmic alkalinization and cell differentiation. Cell acidification by addition of 2-4 mM sodium propionate also blocked TPA-induced U937 cell differentiation. These results suggest that a sustained cell alkalinization mediated by activation of Na+/H+ exchange is essential for TPA-induced differentiation in U937 cells. The increase of cytoplasmic free calcium concentration ([Ca2+]i) by addition of the calcium ionophore ionomycin enhanced TPA-induced alkalinization by increasing the apparent affinity of the Na+/H+ antiporter for intracellular H+. Treatment with ionomycin also potentiated differentiation of U937 cells induced by TPA. This synergism suggests that [Ca2+]i either potentiates the activation of protein kinase C or triggers additional transducing mechanisms. The key events of this interaction occur during the first 30 min of treatment, even though cell differentiation manifests much later.

Properties of the protein kinase C-phorbol ester interaction

The properties of the protein kinase C (PKC)-phorbol ester interaction were highly dependent on assay methods and conditions. Binding to cation-exchange materials or adsorption to gel matrices resulted in PKC that was capable of binding phorbol 12,13-dibutyrate (PDBu). The extraneous interactions were eliminated by measuring phorbol ester binding with a gel filtration chromatography assay in the presence of bovine serum albumin (BSA). In the absence of calcium, free PKC did not bind PDBu or phospholipids. Calcium caused structural changes in PKC which enhanced its interaction with surfaces such as the gel chromatography matrix. While BSA prevented this interaction, it did not interfere with PKC association with acidic phospholipids. Interaction of PKC with phospholipid resulted in two forms of membrane-associated PKC. The initial calcium-dependent and reversible form of membrane-associated PKC was capable of binding PDBu. Both PKC and PDBu were released from this complex by calcium chelation. Sustained interaction with phospholipid vesicles resulted in a PKC-membrane complex that could not be dissociated by calcium chelation and appeared to result from insertion of PKC into the hydrocarbon portion of the phospholipid bilayer. Membrane insertion was observed at calcium concentrations of 2-500 microM and with membrane compositions of 10-50% acidic phospholipid. However, the extent of insertion was dependent on the binding conditions and was promoted by high phospholipid to PKC ratios, high calcium, the presence of phorbol esters, high membrane charge, and long incubations.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinases in neutrophils: a review

In chemotactic factor-stimulated neutrophils, rapid increases of intracellular levels of cyclic AMP, calcium, and diacylglycerol have been observed and may be linked to protein kinase activation. The study of the physiological role and regulation of protein kinases in the neutrophil and the identification of their substrates has provided valuable information on the molecular mechanism of neutrophil activation. The focus of this review is on those aspects of protein kinases that are relevant to neutrophil activation and on the substrate proteins for these protein kinases. The possible role of protein phosphorylation in neutrophil function is also discussed.

Oncogenes, protooncogenes, and signal transduction: toward a unified theory?

This paper has reviewed, in a broad sense, the potential involvement of the oncogenes and their progenitors, the protooncogenes, in signal transduction pathways. The membrane-associated oncogene products appear to be connected with the generation and/or regulation of secondary messengers, particularly those associated with Ca2+/phospholipid-dependent activation of the serine/threonine kinase protein kinase C. Activation of transmembrane receptors, either through binding their native ligand or through point mutations that lead to constitutive expression, results in the expression of their intrinsic tyrosine-specific protein kinases. In PDGF-stimulated cells, this results in the increased turnover of phosphatidylinositols and the subsequent release of IP3 (Habenicht et al., 1981; Berridge et al., 1984). This coincides with activation of a PI kinase activity (Kaplan et al., 1987). Likewise, the fms product, which is the receptor for CSF-1, induces a guanine nucleotide-dependent activation of phospholipase C (Jackowski et al., 1986). Receptor functions are potentially regulated through differential binding of ligands (as proposed with PDGF), through interactions with other receptors, and through the "feedback" regulation mediated by protein kinase C. PDGF stimulation leads to modulation of the EGF receptor through protein kinase C (Bowen-Pope et al., 1983; Collins et al., 1983; Davis and Czech, 1985). Similarly, the neu product becomes phosphorylated on tyrosine residues following treatment of cells with EGF, although the neu protein does not bind EGF itself (King et al., 1988; Stern and Kamps, 1988). The tyrosine kinases of the src family are not receptors themselves, although they may mediate specific receptor-generated signals. The clck product is physically and functionally associated with the T-cell receptors CD4 and CD8, and becomes active upon specific stimulation of cells expressing those markers (Veillette et al., 1988a,b). The precise physiological role of the src family products has not been established, but their kinase activity is intrinsic to that function. The v- and c-src products are hyperphosphorylated during mitosis (Chackalaparampil and Shalloway, 1988), which correlates with periods of reduced cell-to-cell adhesion and communication (Warren and Nelson, 1987; Azarnia et al., 1988). Furthermore, pp60c-src is associated with a PI kinase activity when complexed with MTAg of polyoma virus, suggesting a function in stimulating increased turnover of the phosphatidylinositols (Heber and Courtneidge, 1987; Kaplan et al., 1987).(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of the respiratory burst oxidase in neutrophils: on the role of membrane-derived second messengers, Ca++, and protein kinase C

A major bactericidal mechanism of neutrophils involves activation of the respiratory burst oxidase to generate superoxide (O2-). The oxidase is activated rapidly, often within a minute, in response to extracellular signals such as chemoattractants, inflammatory mediators, and invading microorganisms. Increasing evidence indicates that lipases also respond rapidly, releasing potent regulatory molecules from progenitor lipids. Released molecules include potential regulators of protein kinase C--diacylglycerol (DAG), arachidonate, and sphingosine--and levels of one of these, DAG, frequently correlate with O2- production. In this author's view, the available data implicate DAG and protein kinase C as key factors in the regulation of the respiratory burst. Herein, the array of activating agonists, the generation and function of some lipid-derived mediators, and evidence pertaining to the participation of protein kinase C are reviewed.

Enhancement of phorbol ester-induced protein kinase activity in human neutrophils by platelet-activating factor

We have shown that platelet-activating factor (PAF), a weak primary stimulus for neutrophil superoxide generation, synergistically enhances neutrophil oxidative responses to the tumor promoter phorbol myristate acetate (PMA). Since PMA is known to cause cytosol-to-membrane shift of calcium-activated, phospholipid-dependent protein kinase (protein kinase c, PKC) in human neutrophils, we investigated the role of PAF in modifying PMA-induced PKC activation/translocation. Protein kinase activity was measured as the incorporation of 32P from gamma-32P-ATP into histone H1 induced by enzyme in cytosolic and particulate fractions from sonicated human neutrophils. PAF did not alter the sharp decrease in cytosolic PKC activity induced by PMA. However, in the presence of PAF and PMA, total particulate protein kinase activity increased markedly over that detected in the presence of PMA alone (144 +/- 9 pmoles 32P/10(7)PMN/minute in cells treated with 20 ng/ml PMA compared to 267 +/- 24 pmoles 32P in cells exposed to PMA and 10(-6)M PAF). The increase in total particulate protein kinase activity was synergistic for the two stimuli, required the presence of cytochalasin B during stimulation, and occurred at PAF concentrations of 10(-7) M and above. Both PKC and calcium-, phospholipid-independent protein kinase activities in whole particulate fractions were augmented by PAF as were both activities in detergent-extractable particulate subfractions. PAF did not directly activate PKC obtained from control or PMA-treated neutrophils. However, the PKC-enhancing effect of PAF was inhibited in the absence of calcium during cellular stimulation. PAF also increased particulate protein kinase activity in cells simultaneously exposed to FMLP but the effect was additive for these stimuli. These results suggest that PAF enhances PMA-induced particulate PKC activity by a calcium-dependent mechanism. The enhancing effect of PAF may be directly involved in the mechanism whereby the phospholipid "primes" neutrophils for augmented oxidative responses to PMA.

Tumor-promoting phorbol esters stimulate the proliferation of interleukin-3 dependent cells

To determine whether activation of protein kinase C is involved in the proliferation of interleukin-3 (IL-3) -dependent cells, we examined the effect of tumor-promoting phorbol esters on the in vitro proliferation of the IL-3-dependent cell lines FD and DA-1. The viability of FD and DA-1 cells cultured for 24 hours in 100 nM phorbol myristate acetate (PMA) and 10% FCS was similar to that of cells cultured in 25% WEHI-3 conditioned medium as a source of IL-3, and 10% FCS. FD cells failed to proliferate in concentrations of FCS of up to 50%, while DA-1 cell proliferation was not markedly influenced by FCS. By contrast, PMA promoted the proliferation of FD and DA-1 cells in the absence of FCS and enhanced their proliferation in the presence of 10% FCS, 60- and 20-fold, respectively. Stimulation of proliferation was achieved with as little as 10 nM PMA and was maximal at 100 nM PMA. Low concentrations (0.05-0.1%) of WEHI-3 CM promoted the proliferative response of FD and DA-1 cells to PMA, but at concentrations of WEHI-3 CM greater than 0.8%, no further increment in proliferation was obtained with PMA. As little as 1/2 hour of exposure to phorbol esters was sufficient to cause translocation of protein kinase C from the cytosol to the membranes of DA-1 cells, and 1 hour of exposure to phorbol esters was sufficient to stimulate DNA synthesis. A protein kinase C inhibitor, H-7, at a concentration of 10 microM inhibited phorbol ester-induced stimulation of DA-1 cell proliferation. When DA-1 cells were exposed to the calcium ionophore A23187 in addition to both a phorbol ester and IL-3, their proliferation was enhanced over that stimulated by only the phorbol ester and IL-3. The data indicate that stimulation of proliferation of IL-3-dependent cells involves the activation of protein kinase C.

Differential role of extra- and intracellular calcium in the release of EDRF and prostacyclin from cultured endothelial cells

1. The effects of extracellular Ca2+ on the release of endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2), and on the intracellular free calcium concentration [( Ca2+]i), were studied in cultured bovine aortic endothelial cells. 2. Receptor-mediated stimulation of endothelial cells with bradykinin (10 nM) elicited a transient release of EDRF (assayed by its stimulant effect on purified soluble guanylate cyclase) and of PGI2 (measured by radioimmunoassay for 6-keto prostaglandin F1 alpha). 3. Bradykinin (10 nM) also increased [Ca2+]i (measured with the fluorescent probe indo-1) from 125 +/- 11 nM to 631 +/- 59 nM, with the same time course as for autacoid release. 4. In Ca2+-free medium, [Ca2+]i was still increased by bradykinin but declined faster (within 1 min) to resting levels than in the presence of extracellular Ca2+. 5. PGI2 release was almost completely abolished in Ca2+-free medium. The intracellular calcium antagonist TMB-8 evoked a similar inhibition of PGI2 release. 6. In contrast, bradykinin-induced EDRF release was not significantly affected by TMB-8 but was completely abolished in Ca2+-free medium. 7. When endothelial cells were stimulated with the receptor-independent drug thimerosal (an inhibitor of the enzyme acyl-CoA-lysolecithin-acyl-transferase; 5 microM), a long-lasting release of EDRF (greater than 90 min) and PGI2 (greater than 20 min) was observed. 8. In contrast to bradykinin stimulation, thimerosal-induced autacoid release was associated with only a slight increase of [Ca2+]i to 201 +/- 13 nM after 40 min. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released.

Alpha 1-adrenoceptor-mediated phosphoinositide breakdown and inotropic response in rat left ventricular papillary muscles

alpha 1-Adrenoceptor stimulation of rat left ventricular papillary muscles by phenylephrine in the presence of propranolol resulted in rapid breakdown of phosphatidylinositol 4,5-bisphosphate (PI-4,5-P2) and a triphasic inotropic response in a concentration-dependent manner. The release of inositol trisphosphate (IP3) was maximum within 30 seconds and remained high for at least 30 minutes. The IP3 formation was associated with a rapid, but small, increase in contractile force followed by a transient decline in the contractility prior to the development of a sustained and more pronounced positive inotropic response. Inhibition of PI-4,5-P2 hydrolysis by the alpha 1-adrenergic antagonist prazosin or the PI-4,5-P2 phosphodiesterase inhibitor neomycin blocked all components of the inotropic responses. Combined addition of 2,3-diphosphoglyceric acid, a competitive inhibitor of IP3 phosphatase, with phenylephrine doubled the IP3 formation and potentiated the initial phases of inotropic responses but had no effect on the sustained positive inotropic response. Nifedipine and Mn2+ did not block the transient inotropic responses but inhibited the sustained positive inotropic response. alpha 1-Adrenoceptor stimulation resulted in restoration of slow responses in the high K+-depolarized muscles in the time course similar to that of the development in the sustained positive inotropic response. Addition of phorbol-12,13-dibutyrate alone or in combination with caffeine or A23187 failed to produce a sustained positive inotropic effect, but pretreatment with this phorbol ester (1-100 nM) for 30 minutes resulted in dose-dependent potentiation of alpha 1-adrenoceptor-mediated sustained positive inotropic effect associated with enhanced slow responses. These results suggest that the inotropic effects mediated by cardiac alpha 1-adrenoceptor stimulation occur through the phosphodiesteratic cleavage of PI-4,5-P2, such that IP3 may produce transient inotropic effects by mobilizing intracellular Ca2+, while diacylglycerol, along with cofactors that are also generated on alpha 1-adrenoceptor stimulation, may provoke a sustained positive inotropic effect by potentiating slow Ca2+ channels through activation of protein kinase C.

Effects of TMB-8 and dantrolene on ACTH- and angiotensin-induced steroidogenesis by frog interrenal gland: evidence for a role of intracellular calcium in angiotensin action

The influence of intracellular calcium on the steroidogenic response of adrenocortical tissue to ACTH and angiotensin has been studied in the frog, using a perifusion system technique. The release of corticosterone, aldosterone and prostaglandins in the effluent medium was monitored by specific radioimmunoassays. TMB-8 and dantrolene, two potential blockers of calcium mobilization from intracellular pool(s), were tested. Dantrolene (5 X 10(-5) M) significantly reduced basal and angiotensin-induced corticosterone and aldosterone production but had little effect on ACTH-evoked steroid release. Conversely TMB-8 (10(-4) M) profoundly depressed spontaneous as well as ACTH- and angiotensin II-induced corticosteroid secretion, suggesting that this compound may affect not only calcium mobilization from the endoplasmic reticulum pool but also calcium influx. Adrenal glands perifused with both dantrolene and calcium-free medium showed no response to angiotensin II. Conversely, in calcium-free conditions and in the presence of dantrolene, angiotensin II still caused an increase in prostaglandin synthesis. Taken together, these results indicate that 1) dantrolene is a more specific agent than TMB-8 in inhibiting calcium mobilization from intracellular pool(s); 2) ACTH increases corticosteroidogenesis without inducing mobilization of intracellular calcium; 3) angiotensin II stimulates both the efflux of calcium from the endoplasmic reticulum and the influx of calcium through the plasma membrane; 4) calcium is required after prostaglandin production in the steroidogenic response of frog interrenal gland to angiotensin II.

Divergent effects of co-carcinogenic phorbol esters and a synthetic diacylglycerol on human neutrophil chemokinesis and granular enzyme secretion

The effects of two co-carcinogenic phorbol esters (phorbol myristate acetate (PMA) and phorbol dibutyrate (PDBu] and a synthetic diacylglycerol (OAG, 1-oleoyl-2-acetyl-glycerol), which all stimulate protein kinase C, were compared with two inactive phorbol compounds (4 alpha-phorbol and 4 alpha-phorbol didecanoate (4 alpha-PDD)) on three functional properties of stimulated human polymorphonuclear leukocytes (PMNs): release of granular enzymes lysozyme and beta-glucuronidase, chemokinesis, and changes in cytoplasmic free calcium [Ca2+]i. PMA, PDBu and the diacylglycerol, OAG, all caused a dose-dependent and slow (max by 15 min) release of small amounts of lysozyme with much less beta-glucuronidase and no release of cytoplasmic lactate dehydrogenase. Release was unaffected by removal of extracellular Ca2+. PMA, PDBu and OAG inhibited random movement of the cells, did not cause chemokinesis and induced a slow reduction in the basal [Ca2+]i, as measured by the quin-2 method. PMA, PDBu and OAG increased the capacity of five independently-acting stimulants (N-formyl-Met-Leu-Phe, leukotriene B4, C5a des-Arg, platelet activating factor and A23187) to cause release of lysozyme and beta-glucuronidase but strongly inhibited PMN chemokinesis induced by the same five agents and reduced the stimulant-induced increases in [Ca2+]i. PMA was always more potent than PDBu and much more potent than OAG in eliciting these stimulatory or inhibitory effects on human PMNs. In all tests, 4 alpha-phorbol and 4 alpha-PDD were inactive. The results confirm that stimulation of the diacylglycerol/protein kinase C system in human PMN, either by active phorbol esters or the synthetic diacylglycerol, causes bidirectional effects on human PMN function. In particular, activation of the C-kinase causes inhibition of stimulated neutrophil motility, whereas the secretory functions of the cells are enhanced.

Calcium ionophore A23187 enhances human neutrophil superoxide release, stimulated by phorbol dibutyrate, by converting phorbol ester receptors from a low- to high-affinity state

The calcium ionophore A23187 acted synergistically with phorbol dibutyrate (PDBu) to stimulate human neutrophil superoxide production. A23187 shortened the lag period and markedly increased the initial rate of neutrophil superoxide production induced by suboptimal concentrations of PDBu. 1 microM A23187 reduced the EC50 value for superoxide release from 56 to 8 nM PDBu. This effect of A23187 was correlated with enhanced binding of [3H]PDBu to its receptor and a reduction in the dissociation constant (Kd) from 27 to 10 nM, without altering the apparent total number of phorbol dibutyrate receptors. These actions of A23187 were abolished in the presence of EGTA or TMB-8, confirming a dependence on Ca2+.

In-vitro modulation of protein kinase C activity by environmental chemical pollutants

A number of environmental chemical pollutants have been reported to cause tumors or help in the propagation of tumors in experimental animals. The in-vitro effects of a few chemical contaminants were studied on the histone phosphorylation and 3H Phorbol dibutyrate (PdBu) binding of partially purified Ca2+/phospholipid dependent protein kinase c (PKC) from the brains of Fischer F344 and B6C3F1 mice. The enzyme was prepared by a modified method which gave approximately 75-fold purification. A differential effect of various compounds was observed on the phosphorylation activity and PdBu binding of PKC from rats and mice. The reported tumor promoting ability and effect on protein kinase C activity appeared to be related in the case of the rat enzyme, although causality cannot be inferred.

Features of the translocation of protein kinase C in neutrophils stimulated with the chemotactic peptide f-Met-Leu-Phe

The effects of f-Met-Leu-Phe (fMLP) on neutrophils, i.e. elevation of the levels of cytoplasmic Ca2+ and intramembranous diacylglycerol, would be expected to be accompanied by translocation of protein kinase C (PKC) to the plasmalemma. However, fMLP-induced PKC translocation could hitherto be demonstrated only when cells were additionally treated with cytochalasin B. We show here that treatment of guinea pig neutrophils with fMLP alone does lead to a significant PKC translocation which can be inhibited by pertussis toxin. The translocation can be detected only if the incubation is terminated within 30 sec after addition of fMLP, the termination is rapid, e.g. by application of a freeze clamp-technique, and the concentration of Ca2+ chelators in the buffer used for lysing the cells is low.