Protein kinase inhibitors and blood pressure control in spontaneously hypertensive rats

Regulation of Eosinophil Recruitment and Allergic Airway Inflammation by Tropomyosin Receptor Kinase A

Eosinophilia is a hallmark of allergic airway inflammation (AAI). Identifying key molecules and specific signaling pathways that regulate eosinophilic inflammation is critical for development of novel therapeutics. Tropomycin receptor kinase A (TrkA) is the high-affinity receptor for nerve growth factor. AAI is associated with increased expression of TrkA by eosinophils; however, the functional role of TrkA in regulating eosinophil recruitment and contributing to AAI is poorly understood. This study identifies, to our knowledge, a novel mechanism of eotaxin-mediated activation of TrkA and its role in regulating eosinophil recruitment by using a chemical-genetic approach to specifically inhibit TrkA kinase activity with 1-NM-PP1 in TrkAF592A-knock-in (TrkA-KI) eosinophils. Blockade of TrkA by 1-NM-PP1 enhanced eosinophil spreading on VCAM-1 but inhibited eotaxin-1 (CCL11)-mediated eosinophil migration, calcium flux, cell polarization, and ERK1/2 activation, suggesting that TrkA is an important player in the signaling pathway activated by eotaxin-1 during eosinophil migration. Further, blockade of matrix metalloprotease with BB-94 inhibited eotaxin-1-induced TrkA activation and eosinophil migration, additively with 1-NM-PP1, indicating a role for matrix metalloproteases in TrkA activation. TrkA inhibition in Alternaria alternata-challenged TrkA-KI mice markedly inhibited eosinophilia and attenuated various features of AAI. These findings are indicative of a distinctive eotaxin-mediated TrkA-dependent signaling pathway, which, in addition to other TrkA-activating mediators, contributes to eosinophil recruitment during AAI and suggests that targeting the TrkA signaling pathway to inhibit eosinophil recruitment may serve as a therapeutic strategy for management of eosinophilic inflammation in allergic airway disease, including asthma.

Mechanism of CNP-mediated DG-PKC and IP4 signaling pathway in diabetic rats with gastric motility disorder

In the precedent research conducted by the same team, it concluded that the activities in C-type natriuretic peptide (CNP)/cyclic guanosine monophosphate (cGMP)/cyclic adenosine monophosphate (cAMP)/β-type phospholipase C (PLCβ) pathways of rat antral smooth muscle were changed due to diabetes, which was the key pathogenetic mechanism for diabetic gastric dysmotility. As the follow-on step, this study was designed to probe into the downstream signaling pathway of CNP/PLCβ. The results showed that level of α-type protein kinase C (PKCα),cell membrane to cytoplasm ratio of PKCα, cell membrane to cytoplasmic ratio of βI-type protein kinase C (PKCβI) and level of Phosphor-PKCα (P-PKCα) were significantly reduced in diabetes rat antral smooth muscle samples. The content of tetraphosphate inositol (IP4) in gastric antral smooth muscle of diabetic rats reduced, and the content of diacyl-glycerol (DG) was unchanged. CNP significantly decreased the content of IP4 and DG, this effect was more obvious in diabetic rats. Subsequent to the addition of protein kinase A (PKA) blocker N-[2- (p-Bromocin-namylamino)ethyl]-5 -isoquinolinesulfonamide dihydrochloride (H-89) before CNP treatment, the inhibitory effect of CNP was reduced; subsequent to the addition of protein kinase G (PKG) blocker KT5823 before CNP treatment, the inhibitory effect of CNP was also reduced. With the addition of the combination of H-89 and KT5823 before CNP treatment, the inhibition by CNP could be offset. These results were concluded that CNP inhibited the activity of PKC family in rat smooth muscle and reduced the levels of IP4 and DG through the PKG/PKA-PLCβ pathways, causing inhibited muscular contractions, which may be a key pathogenetic factor for diabetic gastroparesis.

Protein kinase Cα deletion causes hypotension and decreased vascular contractility

AIM

Protein kinase Cα (PKCα) is a critical regulator of multiple cell signaling pathways including gene transcription, posttranslation modifications and activation/inhibition of many signaling kinases. In regards to the control of blood pressure, PKCα causes increased vascular smooth muscle contractility, while reducing cardiac contractility. In addition, PKCα has been shown to modulate nephron ion transport. However, the role of PKCα in modulating mean arterial pressure (MAP) has not been investigated. In this study, we used a whole animal PKCα knock out (PKC KO) to test the hypothesis that global PKCα deficiency would reduce MAP, by a reduction in vascular contractility.

METHODS

Radiotelemetry measurements of ambulatory blood pressure (day/night) were obtained for 18 h/day during both normal chow and high-salt (4%) diet feedings. PKCα mice had a reduced MAP, as compared with control, which was not normalized with high-salt diet (14 days). Metabolic cage studies were performed to determine urinary sodium excretion.

RESULTS

PKC KO mice had a significantly lower diastolic, systolic and MAP as compared with control. No significant differences in urinary sodium excretion were observed between the PKC KO and control mice, whether fed normal chow or high-salt diet. Western blot analysis showed a compensatory increase in renal sodium chloride cotransporter expression. Both aorta and mesenteric vessels were removed for vascular reactivity studies. Aorta and mesenteric arteries from PKC KO mice had a reduced receptor-independent relaxation response, as compared with vessels from control. Vessels from PKC KO mice exhibited a decrease in maximal contraction, compared with controls.

CONCLUSION

Together, these data suggest that global deletion of PKCα results in reduced MAP due to decreased vascular contractility.

A Genetic Response Score for Hydrochlorothiazide Use: Insights From Genomics and Metabolomics Integration

Hydrochlorothiazide is among the most commonly prescribed antihypertensives; yet, <50% of hydrochlorothiazide-treated patients achieve blood pressure (BP) control. Herein, we integrated metabolomic and genomic profiles of hydrochlorothiazide-treated patients to identify novel genetic markers associated with hydrochlorothiazide BP response. The primary analysis included 228 white hypertensives treated with hydrochlorothiazide from the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR) study. Genome-wide analysis was conducted using Illumina Omni 1 mol/L-Quad Chip, and untargeted metabolomics was performed on baseline fasting plasma samples using a gas chromatography-time-of-flight mass spectrometry platform. We found 13 metabolites significantly associated with hydrochlorothiazide systolic BP (SBP) and diastolic BP (DBP) responses (false discovery rate, <0.05). In addition, integrating genomic and metabolomic data revealed 3 polymorphisms (rs2727563 PRKAG2, rs12604940 DCC, and rs13262930 EPHX2) along with arachidonic acid, converging in the netrin signaling pathway (P=1×10(-5)), as potential markers, significantly influencing hydrochlorothiazide BP response. We successfully replicated the 3 genetic signals in 212 white hypertensives treated with hydrochlorothiazide and created a response score by summing their BP-lowering alleles. We found patients carrying 1 response allele had a significantly lower response than carriers of 6 alleles (∆SBP/∆DBP: -1.5/1.2 versus -16.3/-10.4 mm Hg, respectively, SBP score, P=1×10(-8) and DBP score, P=3×10(-9)). This score explained 11.3% and 11.9% of the variability in hydrochlorothiazide SBP and DBP responses, respectively, and was further validated in another independent study of 196 whites treated with hydrochlorothiazide (DBP score, P=0.03; SBP score, P=0.07). This study suggests that PRKAG2, DCC, and EPHX2 might be important determinants of hydrochlorothiazide BP response.

Prenatal testosterone exposure induces hypertension in adult females via androgen receptor-dependent protein kinase Cδ-mediated mechanism

Prenatal exposure to excess testosterone induces hyperandrogenism in adult females and predisposes them to hypertension. We tested whether androgens induce hypertension through transcriptional regulation and signaling of protein kinase C (PKC) in the mesenteric arteries. Pregnant Sprague-Dawley rats were injected with vehicle or testosterone propionate (0.5 mg/kg per day from gestation days 15 to 19, SC) and their 6-month-old adult female offspring were examined. Plasma testosterone levels (0.84±0.04 versus 0.42±0.09 ng/mL) and blood pressures (111.6±1.3 versus 104.5±2.4 mm Hg) were significantly higher in prenatal testosterone-exposed rats compared with controls. This was accompanied with enhanced expression of PKCδ mRNA (1.5-fold) and protein (1.7-fold) in the mesenteric arteries of prenatal testosterone-exposed rats. In addition, mesenteric artery contractile responses to PKC activator, phorbol-12,13-dibutyrate, was significantly greater in prenatal testosterone-exposed rats. Treatment with androgen receptor antagonist flutamide (10 mg/kg, SC, BID for 10 days) significantly attenuated hypertension, PKCδ expression, and the exaggerated vasoconstriction in prenatal testosterone-exposed rats. In vitro exposure of testosterone to cultured mesenteric artery smooth muscle cells dose dependently upregulated PKCδ expression. Analysis of PKCδ gene revealed a putative androgen responsive element in the promoter upstream to the transcription start site and an enhancer element in intron-1. Chromatin immunoprecipitation assays showed that androgen receptors bind to these elements in response to testosterone stimulation. Furthermore, luciferase reporter assays showed that the enhancer element is highly responsive to androgens and treatment with flutamide reverses reporter activity. Our studies identified a novel androgen-mediated mechanism for the control of PKCδ expression via transcriptional regulation that controls vasoconstriction and blood pressure.

Role of PKC-ζ in NADPH oxidase-PKCα-Giα axis dependent inhibition of β-adrenergic response by U46619 in pulmonary artery smooth muscle cells

Treatment of bovine pulmonary artery smooth muscle cells (BPASMCs) with U46619 attenuated isoproterenol caused stimulation of adenyl cyclase activity and cAMP production. Pretreatment with SQ29548 (Tp receptor antagonist), apocynin (NADPH oxidase inhibitor) and Go6976 (PKC-α inhibitor) eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with SQ29548 and apocynin prevented U46619 induced increase in NADPH oxidase activity, PKC-α activity and Giα phosphorylation. However, pretreatment with CZI, a PKC-ζ inhibitor, markedly, but not completely, inhibited U46619 induced increase in NADPH oxidase activity, PKC-α activity, Giα phosphorylation and also significantly eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with Go6976 inhibited U46619 induced increase in Giα phosphorylation, but not PKC-ζ activity and NADPH oxidase activity. Pretreatment with pertussis toxin eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity without any discernible change in PKC-ζ, NADPH oxidase and PKC-α activities. Transfection of the cells with Tp, PKC-ζ and PKC-α siRNA duplexes corroborate the findings observed with their respective pharmacological inhibitors on the responses produced by U46619. Taken together, we suggest involvement of PKC-ζ in U46619 caused attenuation of isoproterenol stimulated β-adrenergic response, which is regulated by NADPH oxidase-PKCα-Giα axis in pulmonary artery smooth muscle cells.

Possible role of brain salt-inducible kinase 1 in responses to central sodium in Dahl rats

In Dahl salt-sensitive (S) rats, Na+ entry into the cerebrospinal fluid (CSF) and sympathoexcitatory and pressor responses to CSF Na+ are enhanced. Salt-inducible kinase 1 (SIK1) increases Na+/K+-ATPase activity in kidney cells. We tested the possible role of SIK1 in regulation of CSF [Na+] and responses to Na+ in the brain. SIK1 protein and activity were lower in hypothalamic tissue of Dahl S (SS/Mcw) compared with salt-resistant SS.BN13 rats. Intracerebroventricular infusion of the protein kinase inhibitor staurosporine at 25 ng/day, to inhibit SIK1 further increased mean arterial pressure (MAP) and HR but did not affect the increase in CSF [Na+] or hypothalamic aldosterone in Dahl S on a high-salt diet. Intracerebroventricular infusion of Na+-rich artificial CSF caused significantly larger increases in renal sympathetic nerve activity, MAP, and HR in Dahl S vs. SS.BN13 or Wistar rats on a normal-salt diet. Intracerebroventricular injection of 5 ng staurosporine enhanced these responses, but the enhancement in Dahl S rats was only one-third that in SS.BN13 and Wistar rats. Staurosporine had no effect on MAP and HR responses to intracerebroventricular ANG II or carbachol, whereas the specific protein kinase C inhibitor GF109203X inhibited pressor responses to intracerebroventricular Na+-rich artificial CSF or ANG II. These results suggest that the SIK1-Na+/K+-ATPase network in neurons acts to attenuate sympathoexcitatory and pressor responses to increases in brain [Na+]. The lower hypothalamic SIK1 activity and smaller effect of staurosporine in Dahl S rats suggest that impaired activation of neuronal SIK1 by Na+ may contribute to their enhanced central responses to sodium.

Etomidate reduces glutamate uptake in rat cultured glial cells: involvement of PKA

BACKGROUND AND PURPOSE

Glutamate is the main excitatory neurotransmitter in the vertebrate CNS. Removal of the transmitter from the synaptic cleft by glial and neuronal glutamate transporters (GLTs) has an important function in terminating glutamatergic neurotransmission and neurological disorders. Five distinct excitatory amino-acid transporters have been characterized, among which the glial transporters excitatory amino-acid transporter 1 (EAAT1) (glutamate aspartate transporter) and EAAT2 (GLT1) are most important for the removal of extracellular glutamate. The purpose of this study was to describe the effect of the commonly used anaesthetic etomidate on glutamate uptake in cultures of glial cells.

EXPERIMENTAL APPROACH

The activity of the transporters was determined electrophysiologically using the whole cell configuration of the patch-clamp recording technique.

KEY RESULTS

Glutamate uptake was suppressed by etomidate (3-100 microM) in a time- and concentration-dependent manner with a half-maximum effect occurring at 2.4+/-0.6 microM. Maximum inhibition was approximately 50% with respect to the control. Etomidate led to a significant decrease of V(max) whereas the K(m) of the transporter was unaffected. In all cases, suppression of glutamate uptake was reversible within a few minutes upon washout. Furthermore, both GF 109203X, a nonselective inhibitor of PKs, and H89, a selective blocker of PKA, completely abolished the inhibitory effect of etomidate.

CONCLUSION AND IMPLICATIONS

Inhibition of glutamate uptake by etomidate at clinically relevant concentrations may affect glutamatergic neurotransmission by increasing the glutamate concentration in the synaptic cleft and may compromise patients suffering from acute or chronic neurological disorders such as CNS trauma or epilepsy.

Rapid increase of glial glutamate uptake via blockade of the protein kinase A pathway

Glutamate is the main excitatory neurotransmitter in the vertebrate central nervous system. Removal of this transmitter from the synaptic cleft by glial and neuronal transporter systems plays an important role in terminating glutamatergic neurotransmission. The effects of different activators and blockers of PKA and PKC on glutamate uptake were studied in primary glial cells cultivated from the rat cortex using the patch-clamp recording technique and immunocytochemical methods. GF 109203X enhances glutamate-induced membrane currents in a concentration- and time-dependent manner. After pre-application for 40 s the maximal transport capacity was increased by 30-80%. The estimated Km-value of the transport system did not change after drug application and the enhanced glutamate uptake was reversible within a few minutes upon washout. Activators and blockers of the PKC pathway did not affect glutamate uptake, whereas H89, a selective blocker of PKA, mimicked the effects of GF 109203X, indicating involvement of the protein kinase A pathway. The GF 109203X-induced increase in transport capacity is likely to be mediated by GLAST since the GLT-1 selective blocker dihydrokainate was unable to block basal or stimulated glutamate uptake. Furthermore, the increase in transport activity may well be based on an increase in cell surface expression of the transporter protein since preincubation with cytochalasin-B, a protein that blocks actin polymerization, almost completely abolished the effect of GF 109203X and H89. These results indicate that GF 109203X and H89 enhance glial glutamate uptake via blockade of the PKA. The described effect may affect glutamatergic neurotransmission by reducing the glutamate concentration in the synaptic cleft.

Mice lacking protein kinase C beta present modest increases in systolic blood pressure and NH4Cl-induced metabolic acidosis

The conventional protein kinase C isoenzyme beta (PKC-beta) is expressed in various structures of mouse kidney. To get insights into the function, PKC-beta knockout (-/-) and wild-type (+/+) mice were studied. Under basal conditions, PKC-beta-/- mice exhibited a higher systolic blood pressure (in awake mice), normal plasma concentrations of Na+ and K+, and normal plasma pH. Urine osmolality and 24-hour excretion of fluid, Na+, K+ and albumin were not different between genotypes, but urine pH was more alkaline in PKC-beta-/- mice. Inulin clearance experiments under anesthesia confirmed a higher systolic blood pressure and revealed normal glomerular filtration rate and fractional excretion of fluid, Na+ and K+ in PKC-beta-/- mice. The ability to restrict renal Na+ excretion in response to a low Na+ diet was unaltered in PKC-beta-/- mice. Chronic acid loading (NH4Cl) did not affect blood pH in PKC-beta+/+ mice, but induced a modest metabolic acidosis in PKC-beta-/- mice. In conclusion, first evidence is presented that (i) PKC-beta contributes to the regulation of arterial blood pressure, and (ii) PKC-beta is required for normal acid-base balance, which may relate to its expression and function in intercalated cells of the collecting duct.

Protein kinase C activation-induced increases of neural activity are enhanced in the hypothalamus of spontaneously hypertensive rats

We have previously reported that some neurons in the anterior hypothalamic area (AHA) are tonically activated by endogenous angiotensins in rats and that activities of these angiotensin II-sensitive neurons in the AHA are enhanced in spontaneously hypertensive rats (SHR). In addition, neural activations induced by both angiotensin II and glutamate were enhanced in the AHA of SHR. In this study, we examined whether intracellular neural activation mechanisms via protein kinase C (PKC) and a potassium channel are altered in angiotensin II-sensitive neurons in the AHA of SHR. Male 15- to 16-week-old SHR and age-matched Wistar-Kyoto rats (WKY) and Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Pressure application of the PKC activator phorbol 12-myristate 13-acetate (PMA) onto angiotensin II-sensitive neurons in the AHA of Wistar rats increased their firing rate. The increase of unit activity by PMA was inhibited by the potent inhibitor of PKC, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), but not by the weak PKC inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide hydrochloride (HA1004). The increase of unit firing by PMA was enhanced in SHR as compared with WKY. Pressure application of H-7 alone decreased the basal firing activity of angiotensin II-sensitive neurons in SHR but not in WKY. HA1004 did not affect the basal firing activity of angiotensin II-sensitive neurons in SHR. Angiotensin II-induced increases of firing rate in AHA neurons were inhibited by H-7 and the inhibition by H-7 was enhanced in SHR as compared with WKY. Pressure application of 4-aminopyridine, a blocker of the transient potassium current, onto angiotensin II-sensitive neurons increased their firing rate and the increase of unit firing rate was almost the same in WKY and SHR. These findings indicate that activation of PKC increases neural activity in angiotensin II-sensitive neurons in the AHA and that this PKC activation-induced increase of neural activity is enhanced in the AHA of SHR. It seems likely that the enhanced PKC activation effect is responsible for the enhanced basal neural activity seen in the AHA of SHR.

High-performance liquid chromatographic analysis of staurosporine in vivo. Its translocation and pharmacokinetics in rats

The protein kinase inhibitor staurosporine (Stsp) has been used extensively to study physiological functions, biochemical mechanisms, and cancer therapy. Using an HPLC assay for Stsp developed in our laboratory, we find that only 0.7% of Stsp remains in circulating blood of rats 5 min after injection. In vitro, Stsp is adsorbed to red blood cells (RBC) weakly and reversibly. In vivo, all but 1.2-2.5% of Stsp injected is adsorbed by the heart and lungs in one passage through them, indicating that the endothelium acts as a major Stsp sink. Following initial adsorption, pharmacokinetic studies demonstrated that Stsp had a half-life of 51.6 min in plasma and 75.3 min in RBC. Thus, plasma Stsp was in the cancer therapy range of 1-10 ng/ml for 2.7 h following a bolus injection. This data indicates that a bolus injection of Stsp must be followed by a continuous infusion of low Stsp concentration for several days to produce the G1 arrest in cells necessary to stop cell proliferation.

Enalapril induces regression of cardiac hypertrophy and normalization of pHi regulatory mechanisms

Intracellular pH is under strict control in myocardium; H+ are extruded from the cells by sodium-dependent mechanisms, mainly Na+/H+ exchanger and Na+/HCO3- symport, whereas Na+-independent Cl-/HCO3- exchanger extrudes bases on intracellular alkalinization. Hypertrophic myocardium from spontaneously hypertensive rats (SHR) exhibits increased Na+/H+ exchange activity that is accompanied by enhanced extrusion of bases through Na+-independent Cl-/HCO3- exchange. The present experiments were designed to investigate the effect of enalapril-induced regression of cardiac hypertrophy on the activity of these exchangers. Male SHR and normotensive Wistar-Kyoto rats (WKY) received enalapril maleate (20 mg/kg per day) in the drinking water for 5 weeks. Gender- and age-matched SHR and WKY were used as untreated controls. Enalapril treatment significantly reduced systolic blood pressure in SHR and completely regressed cardiac hypertrophy. Na+/H+ activity was estimated in terms of both steady pHi value in HEPES buffer and the rate of pHi recovery from CO2-induced acid load. Na+-independent Cl-/HCO3- activity was assessed by measuring the rate of pHi recovery from intracellular alkalinization produced by trimethylamine exposure. Regression of cardiac hypertrophy was accompanied by normalization of Na+/H+ and Na+-independent Cl-/HCO3- exchange activities. Inhibition of protein kinase C (PKC) activity with chelerythrine (10 mmol/L) or calphostin C (50 nmol/L) returned both exchange activities to normal values. These results show that angiotensin-converting enzyme inhibition normalizes the enhanced activity of both exchangers while regressing cardiac hypertrophy. Because normalization of exchange activities could be also achieved by PKC inhibition, the data would suggest that PKC-dependent mechanisms play a significant role in the increased ion exchange activities of hypertrophic myocardium and in their normalization by angiotensin-converting enzyme inhibition.

No prevention of ischemic preconditioning by the protein kinase C inhibitor staurosporine in swine

The delay of infarct size development by ischemic preconditioning involves the activation of protein kinase C in rats and rabbits. In dogs the role of protein kinase C in ischemic preconditioning is controversial. We investigated whether or not the activation of protein kinase C is a prerequisite for ischemic preconditioning in swine. Swine were used, since they are large mammals and since infarct development in this species, due to the lack of an innate collateral circulation, is similar to that in humans. In 20 enflurane-anesthetized swine, the proximal left anterior descending coronary artery was cannulated and perfused from an extracorporeal circuit. The impact of continuous intracoronary infusion of 10(-7) mol/L staurosporine, a potent protein kinase C inhibitor, on global and regional myocardial function (sonomicrometry), subendocardial blood flow (ENDO, microspheres), and infarct size (IS, triphenyltetrazolium chloride staining after 120 minutes of reperfusion) was analyzed. Staurosporine (10(-7) mol/L) abolished the 1.6-fold increase in coronary arterial resistance in response to 10(-6) mol/L IC 4 beta-phorbol 12-myristate 13-acetate, a potent protein kinase C activator. In the presence of staurosporine, 90 minutes of low-flow ischemia at an ENDO of 0.05 +/- 0.04 (mean +/- SD) mL.min-1.g-1 resulted in an IS of 12.5 +/- 8.6% (n = 10) of the area at risk. Also, in the presence of staurosporine, ischemic preconditioning by a cycle of 10 minutes of low-flow ischemia followed by 15 minutes reperfusion before the 90 minutes sustained ischemic period (ENDO, 0.05 +/- 0.03 mL.min-1.g-1) reduced IS to 3.3 +/- 3.4% (n = 10, P < .05). The protein kinase C inhibitor staurosporine does not prevent ischemic preconditioning in swine.

Ca(2+)-dependent mitogen-activated protein kinase activation in spontaneously hypertensive rat vascular smooth muscle defines a hypertensive signal transduction phenotype

The mechanisms responsible for altered vascular smooth muscle cell (VSMC) function in hypertension remain unknown. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, there are multiple abnormalities in VSMC function, including increased growth, Na(+)-H+ exchange, and increased signal transduction by protein kinase C. The family of kinases termed mitogen-activated protein (MAP) kinases has recently been shown to be essential mediators of growth factor signal transduction. In the present study, alterations in MAP kinase function in the hypertensive phenotype were investigated using early-passage SHR and Wistar-Kyoto (WKY) VSMCs stimulated with angiotensin II (Ang II, 100 nmol/L) or platelet-derived growth factor-BB (PDGF-BB, 10 ng/mL). MAP kinase activity was measured by in-gel kinase assays and Western blot analysis. Two differences between SHR and WKY rats were observed for Ang II-mediated MAP kinase activation: (1) Inactivation after Ang II stimulation was more rapid in SHR than WKY VSMCs. (2) Activity in SHR VSMCs showed a greater dependence on Ca2+ mobilization, since chelation of intracellular Ca2+ with BAPTA inhibited maximal activity by 95% in SHR VSMCs but by only 50% in WKY VSMCs. In contrast to the results with Ang II, no differences in PDGF-stimulated MAP kinase activity were observed. These findings establish activation of MAP kinase by Ang II as a feature that distinguishes SHR VSMCs from WKY VSMCs and suggest that differences in regulation of MAP kinase signaling may alter cellular events that are increased in the SHR genetic model of hypertension.

Phorbol ester activation of the rat vascular myocyte Na(+)-H(+) exchanger isoform 1

Vascular myocytes from the spontaneously hypertensive rat (SHR) demonstrate elevated Na(+)-H(+) exchanger activity associated with increased cell proliferation and hyperresponsiveness to agonists such as phorbol esters. Since the Na(+)-H(+) exchanger isoform 1 (NHE-1) is stimulated by protein kinase C, we have investigated the effects of phorbol esters on NHE-1 activity and its phosphorylation in vascular myocytes of these rats. SHR cells demonstrated a larger alkalinization response to 12-O-tetradecanoylphorbol 13-acetate than Wistar-Kyoto rat (WKY) cells. Kinetic analyses indicated that whereas 12-O-tetradecanoylphorbol 13-acetate increased the maximal transport capacity of NHE-1 in both cell types, affinity for H+ was increased in WKY cells and cooperativity for H+ at the internal modifier site was reduced in SHR cells. In neither cell type was the subcellular distribution of NHE-1 altered by phorbol ester stimulation. NHE-1 phosphorylation was markedly reduced in WKY cells stimulated by the phorbol ester, an effect abolished by inhibition of protein kinase C. In contrast, NHE-1 phosphorylation in quiescent SHR cells was approximately double that of WKY cells and was reduced after phorbol ester treatment. Inhibition of protein kinase C in SHR cells led to a marked elevation of NHE-1 phosphorylation that was not associated with a change in the exchanger activity, but WKY cells exhibited a small, insignificant rise in NHE-1 phosphorylation. Thus, the kinetic responses of NHE-1 to phorbol esters in vascular myocytes of these rat strains are different, the changes in exchanger kinetics of SHR resembling those described in human hypertension. NHE-1 phosphorylation has an inverse relationship with protein kinase C activity. However, modulation of NHE-1 phosphorylation may not be associated with concurrent alterations in activity, indicating a role for non-phosphorylation-dependent mechanisms.

Na(+)-H+ exchanger isoform 1 phosphorylation in normal Wistar-Kyoto and spontaneously hypertensive rats

Increased activity of the cellular Na(+)-H+ exchanger (NHE) has been documented in various cell types in essential hypertension and in vascular myocytes of the spontaneously hypertensive rat (SHR). The mechanism underlying this abnormality is unclear. Because the NHE can be activated by phosphorylation, we examined phosphorylation of the Na(+)-H+ exchanger isoform 1 (NHE-1) as one possible mechanism for its increased turnover number in cultured vascular myocytes of the SHR. A polyclonal rabbit antibody against a fusion protein consisting of beta-galactosidase and the C-terminus of NHE-1 was used to immunoprecipitate 32P-labeled NHE-1 from cell extracts of SHR and Wistar-Kyoto (WKY) rat vascular myocytes in the absence and presence of 10% fetal calf serum. Immunoprecipitates were separated by SDS-PAGE, and 32P-labeled NHE-1 was quantified from autoradiographs. Similar amounts of NHE-1 protein were detected on Western blots of the cultured vascular myocytes from SHR and WKY rats. In quiescent cells, NHE-1 was significantly more phosphorylated in SHR myocytes than in WKY myocytes (2.17 +/- 0.06-fold enhancement [mean +/- SEM]; P < .001, n = 8). The addition of fetal calf serum to quiescent cells had no significant effect on the phosphorylation of NHE-1 in SHR myocytes. However, NHE-1 phosphorylation fell transiently in serum-treated WKY myocytes, with recovery to control levels after 20 minutes. Measurement of NHE activity using fluorometry confirmed elevated activity in the quiescent SHR myocytes compared with WKY myocytes. Fetal calf serum led to further enhancement of NHE activity in both cell types. These findings suggest that the increased NHE activity in quiescent SHR myocytes may be correlated with enhanced NHE-1 phosphorylation and that serum stimulates NHE activity in both cell types without a further increase in total NHE-1 phosphorylation, indicating a role for non-phosphorylation-dependent regulatory mechanisms.

Decreased sensitivity of aorta from hypertensive rats to vasorelaxation by tyrphostin

The role of protein tyrosine kinases (PTKs) in vascular smooth muscle (VSM) contraction was examined in spontaneously hypertensive rats (SHRs). Aorta from SHRs was hyperresponsive to PTK-mediated contraction relative to normotensive Wistar-Kyoto rats (WKYs). Aorta from SHR was also hyporesponsive to vasorelaxation by tyrphostin, a selective inhibitor of PTKs. Further, we found alterations in PTK activity in aorta from SHRs. PDGF stimulated PTK activity to a greater extent in the SHR. Tyrphostin inhibited PDGF-induced PTK stimulation in both strains, however, activity returned to basal levels in the WKY only. The results suggest that PTKs may be involved in VSM contraction and in the development of hypertension.

Gamma-interferon corrects aberrant protein kinase C levels and immunosuppression in the spontaneously hypertensive rat

The effects of gamma-interferon (gamma-IFN) on protein kinase C (PKC) levels and immunosuppression in the spontaneously hypertensive rat (SHR) were examined. First, an abnormal PKC distribution was found in spleen, thymus and aorta from SHRs relative to normotensive controls. Biweekly injections of rat recombinant gamma-IFN (1000 U/kg) restored basal or resting PKC levels to those found in normotensive Wistar-Kyoto (WKY) rats. We also examined the effects of in vivo gamma-IFN treatment on nuclear PKC (nPKC) activation in purified, isolated splenocyte nuclei. It was found that basal nPKC levels were higher in untreated SHRs than gamma-IFN SHRs or WKYs. Also, while nuclei from untreated SHRs were relatively unresponsive to various immunoreactive substances and PKC activators, gamma-IFN treatment significantly restored activity. Last, the proliferative response to mitogen challenge of isolated splenocytes from untreated SHRs, gamma-IFN-treated SHRs and WKYs was studied. Although gamma-IFN treatment did not restore the proliferative response to that of WKYs, the mitogen response was significantly enhanced by treatment with gamma-IFN. The data show that gamma-IFN acts to restore normal immune function and corrects aberrant PKC levels and adds to the growing body of knowledge suggesting a role for immune dysfunction in the etiology of hypertension.

Trends in the search for bioactive microbial metabolites

Bioactive microbial metabolites are attracting increasing attention as useful agents for medicine, veterinary medicine, agriculture, and as unique biochemical tools. A review of the current trends in the discovery of new metabolites shows that the number of active compounds with non-antibiotic type of activity has increased, resulting in an expansion of the variety of bioactivity of microbial metabolites. Factors that contribute to the increased rate of discovery include: development of new methods for activity measurement, exploitation of novel groups of microorganisms as sources of active compounds, new directions for chemical modification, and incorporation of newer knowledge of biotechnology into screening systems. To exemplify this, typical screening methods, and chemical and biological properties of several bioactive compounds obtained by these methods are discussed.

The expanded horizon for microbial metabolites--a review

Modern screening methods have been used for a variety of new natural products. By taking advantage of the side effects of erythromycin, a derivative, EM523, and several related substances (motilides) have been synthesized. These compounds are agonists of the peptide hormone, motilin. By screening for microbial metabolites which may substitute for biologically active peptides, we discovered lactacystin. It has nerve growth-factor-like activity and induces differentiation in mouse neuroblastoma Neuro2A cells. An inhibitor of protein kinase, staurosporine, a microbial alkaloid found by chemical screening, has a variety of pharmacological activities, such as the relaxation of rabbit aortic strips and the inhibition of changes in platelet shape induced with phorbol myristate acetate. Triacsin, an inhibitor of acetyl-CoA synthetase, which was isolated from Streptomyces sp. SK-1894, potentiated platelet-activating factor production of A23187-treated rat polymorphonuclear leukocytes. Phthoxazolin, an inhibitor of cellulose biosynthesis isolated from Streptomyces sp. OM-5714, inhibited the growth of velvet leaf when treated after its emergence. These products provide examples of the possible utility of newly discovered microbial metabolites.

Vascular protein kinase C in Wistar-Kyoto and spontaneously hypertensive rats

Phorbol esters which activate protein kinase C (PKC) produced concentration-related force development in aorta from spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY); all were 2-7 x more potent in SHR. However, total PKC activity in aortas, as well as carotid, caudal and renal arteries, was not different, when SHR was compared with WKY. Binding of phorbol dibutyrate to particulate aortic PKC was similar in SHR and WKY (same apparent Kd and Bmax values), as was potency for displacement of phorbol dibutyrate by phorbol myristate acetate. Furthermore, there was no difference in potency with staurosporine, H-7, and calmidazolium in inhibiting SHR and WKY aortic PKC. These data demonstrate enhanced contractile sensitivity to PKC-activating phorbol esters in SHR aortic smooth muscle that is not related to activity, phorbol ester binding, or sensitivity to inhibitors when SHR PKC is compared with WKY PKC. Thus, signal transduction events distal to PKC activation may be responsible for enhanced vascular contractile sensitivity to phorbol esters in SHR.

Attenuation of anaphylactic shock and related mortality in guinea-pigs after administration of a potent protein kinase inhibitor, K252a

We examined whether protein kinases have a role in the expression of anaphylactic shock (AS). Guinea-pigs sensitized to ovalbumin were administered i.p. saline (control) or 10 micrograms/kg K252a, a potent protein kinase inhibitor, 30 min before challenge. The development of AS and mortality was observed for the next 2 h. In the K252a-treated group the incidence of AS fell to 53% from 100%, the maximum intensity was 62% less than the control, and mortality dropped to 16% from 50% of the animals. We suggest that protein kinases are involved in the expression of AS, and that inhibitors of these enzymes may protect against the symptoms of AS and allergy.

Effects of a phorbol ester and staurosporine on electro- and pharmacomechanical coupling in a resistance artery

We examined the role of protein kinase-C in contractile responses of small arteries of the rat by stimulating and inhibiting protein kinase-C with phorbol myristate acetate and staurosporine, respectively. The experiments were performed in isolated mesenteric resistance arteries that had been sympathectomized and mounted for recording of isometric force development. Phorbol myristate acetate (i) at concentrations lower than 3 nM increased sensitivity for the contractile effect of potassium, but not for the effect of noradrenaline or BAY-K8644, (ii) at concentrations higher than 30 nM increased the sensitivity of depolarized vessels to extracellular calcium and (iii) at concentrations higher than 30 nM induced a contractile effect that depended on the presence of extracellular calcium and that was reduced by the calcium antagonist felodipine. Neither the phorbol ester nor staurosporine affected contractile responses to caffeine in calcium-free solution. Staurosporine (10 nM) reduced the response of resistance arteries to potassium but not to noradrenaline. These results are in agreement with direct observations by others that protein kinase-C plays a role in the activation of voltage-operated calcium channels. Protein kinase-C could participate in this way in electro-mechanical coupling in resistance arterial smooth muscle and, when strongly activated, sensitize the contractile apparatus to calcium.