Identification of protein kinase C isoforms in rat mesenteric small arteries and their possible role in agonist-induced contraction

Oxidative and Nitrous Stress Underlies Vascular Malfunction Induced by Ionizing Radiation and Diabetes

Oxidative stress results from the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in quantities exceeding the potential activity of the body's antioxidant system and is one of the risk factors for the development of vascular dysfunction in diabetes and exposure to ionizing radiation. Being the secondary products of normal aerobic metabolism in living organisms, ROS and RNS act as signaling molecules that play an important role in the regulation of vital organism functions. Meanwhile, in high concentrations, these compounds are toxic and disrupt various metabolic pathways. The various stress factors (hyperglycemia, gamma-irradiation, etc.) trigger free oxygen and nitrogen radicals accumulation in cells that are capable to damage almost all cellular components including ion channels and transporters such as Na+/K+-ATPase, BKCa, and TRP channels. Vascular dysfunctions are governed by interaction of ROS and RNS. For example, the reaction of ROS with NO produces peroxynitrite (ONOO-), which not only oxidizes DNA, cellular proteins, and lipids, but also disrupts important signaling pathways that regulate the cation channel functions in the vascular endothelium. Further increasing in ROS levels and formation of ONOO- leads to reduced NO bioavailability and causes endothelial dysfunction. Thus, imbalance of ROS and RNS and their affect on membrane ion channels plays an important role in the pathogenesis of vascular dysfunction associated with various disorders.

Protein Kinase C Downregulation Enhanced Extracellular Ca2+-Induced Relaxation of Isolated Mesenteric Arteries from Aged Dahl Salt-Sensitive Rats

The Ca²⁺-sensing receptor (CaSR) detects small changes in extracellular calcium (Ca²⁺ _e) concentration ([Ca²⁺]_e) and transduces the signal into modulation of various signaling pathways. Ca²⁺-induced relaxation of isolated phenylephrine-contracted mesenteric arteries is mediated by the CaSR of the perivascular nerve. Elucidation of the regulatory mechanisms involved in vascular CaSR signaling may provide insights into the physiologic functions of the receptor and identify targets for the development of new treatments for cardiovascular pathologies such as hypertension. Protein kinase Cα (PKCα) is a critical regulator of multiple signaling pathways and can phosphorylate the CaSR leading to receptor desensitization. In this study, we used automated wire myography to investigate the effects of CaSR mutation and small-interfering RNA downregulation of PKCα on CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive (SS) rats on a low-salt diet. The data showed minimal relaxation responses of arteries to Ca²⁺ _e in wild-type (SS) and CaSR mutant (SS-Casr^em1Mcwi) rats. Mutation of the CaSR gene had no significant effect on relaxation. PKCα expression was similar in wild-type and mutant rats, and small-interfering RNA downregulation of PKCα and/or inhibition of PKC with the Ca²⁺-sensitive Gӧ 6976 resulted in a >80% increase in relaxation. Significant differences in EC₅₀ values were observed between treated and untreated controls (P < 0.05 analysis of variance). The results indicate that PKCα plays an important role in the regulation of CaSR-mediated relaxation of mesenteric arteries, and its downregulation or pharmacological inhibition may lead to an increased Ca²⁺ sensitivity of the receptor and reversal of age-related changes in vascular tone. SIGNIFICANCE STATEMENT: G protein-coupled CaSR signaling leads to the regulation of vascular tone and may, therefore, play a vital role in blood pressure regulation. The receptor has several PKC phosphorylation sites in the C-terminal intracellular tail that mediate desensitization. We have previously shown that activation of the CaSR in neuronal cells leads to PKC phosphorylation, indicating that protein kinase C is an important regulator of CaSR function. Therefore, PKC in the CaSR signaling pathway in mesenteric arteries is a potential target for the development of new therapeutic approaches to treat hypertension and age-related vascular dysfunction. The present studies show that small-interfering RNA downregulation of PKCα and pharmacological inhibition of PKC enhanced CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive rats.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Role of PKCδ in Enhanced Expression of Gqα/PLCβ1 Proteins and VSMC Hypertrophy in Spontaneously Hypertensive Rats

Gqα signaling has been implicated in cardiac hypertrophy. In addition, angiotensin II (Ang II) was also shown to induce its hypertrophic effect through Gqα and PKCδ activation. We recently showed the role of enhanced expression of Gqα/PLCβ1 proteins in vascular smooth muscle cell (VSMC) hypertrophy, however, the role of PKCδ in VSMC hypertrophy in animal model is still lacking. The present study was therefore undertaken to examine the role of PKCδ and the associated signaling mechanisms in VSMC hypertrophy using 16-week-old spontaneously hypertensive rats (SHR). VSMC from 16-week-old SHR exhibited enhanced phosphorylation of PKCδ-Tyr311 and increased protein synthesis, marker of hypertrophy, as compared to WKY rats which was attenuated by rottlerin, an inhibitor of PKCδ. In addition, knocking down of PKCδ by PKCδ-siRNA also attenuated enhanced protein synthesis in VSMC from SHR. Furthermore, rottlerin attenuated the increased production of superoxide anion, NAD(P)H oxidase activity, increased expression of Gqα, phospholipase C (PLC)β1, insulin like growth factor-1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) proteins in VSMC from SHR. In addition, the enhanced phosphorylation of c-Src, PKCδ-Tyr311, IGF-1R, EGFR and ERK1/2 exhibited by VSMC from SHR was also attenuated by rottlerin. These results suggest that VSMC from SHR exhibit enhanced activity of PKCδ and that PKCδ is the upstream molecule of reactive oxygen species (ROS) and contributes to the enhanced expression of Gqα and PLCβ1 proteins and resultant VSMC hypertrophy involving c-Src, growth factor receptor transactivation and MAP kinase signaling.

α1 -Adrenoceptor activation of PKC-ε causes heterologous desensitization of thromboxane receptors in the aorta of spontaneously hypertensive rats

BACKGROUND AND PURPOSE

In the aorta of adult spontaneously hypertensive (SHR), but not in that of normotensive Wistar-Kyoto (WKY), rats, previous exposure to phenylephrine inhibits subsequent contractions to PGE2 . The present experiments were designed to examine the mechanism(s) underlying this inhibition.

EXPERIMENTAL APPROACH

Isometric tension was measured in isolated rings of SHR and WKY aortae. Gene expression and protein presence were measured by quantitative real-time PCR and Western blotting respectively.

KEY RESULTS

In aorta of 18 weeks SHR, but not age-matched WKY, pre-exposure to phenylephrine inhibited subsequent contractions to PGE2 that were mediated by thromboxane prostanoid (TP) receptors. This inhibition was not observed in preparations of pre-hypertensive 5-week-old SHR, and was significantly larger in those of 36- than 18-week-old SHR. Pre-exposure to the PKC activator, phorbol 12,13-dibutyrate, also inhibited subsequent contractions to PGE2 in SHR aortae. The selective inhibitor of PKC-ε, ε-V1-2, abolished the desensitization caused by pre-exposure to phenylephrine. Two molecular PKC bands were detected and their relative intensities differed in 36-week-old WKY and SHR vascular smooth muscle. The mRNA expressions of PKC-α, PKC-ε, PK-N2 and PKC-ζ and of G protein-coupled kinase (GRK)-2, GRK4 and β-arrestin2 were higher in SHR than WKY aortae.

CONCLUSIONS AND IMPLICATIONS

These experiments suggest that in the SHR but not the WKY aorta, α1 -adrenoceptor activation desensitizes TP receptors through activation of PKC-ε. This heterologous desensitization is a consequence of the chronic exposure to high arterial pressure.

Maternal high-salt diets affected pressor responses and microvasoconstriction via PKC/BK channel signaling pathways in rat offspring

SCOPE

High-salt (HS) intake is linked to hypertension, and prenatal exposure to maternal HS diets may have long-term impact on cardiovascular systems. The relationship between HS diets and cardiovascular disease has received extensive attention. This study determined pressor responses and microvessel functions in the adult offspring rats exposed to prenatal HS.

METHODS AND RESULTS

The offspring of 5-month old as young adults in rats were used. Blood pressure, vascular tone, intracellular Ca(2+), and BK channels in mesenteric arteries were measured in the offspring. Phenylephrine (Phe)-induced pressor responses were significantly higher in the prenatal HS offspring. Vessel tension and intracellular Ca(2+) concentrations associated with Phe-induced pressor responses were increased in the mesenteric arteries of the HS offspring. PKC α- and δ-isoforms were upregulated in mesenteric arteries of the HS offspring. The enhanced Phe-mediated vascular activity was linked to the altered PKC-modulated BK channel functions.

CONCLUSION

The results suggested that prenatal exposure to HS altered microvascular activity probably via changes in PKC/BK signaling pathways, which may lead to increased risks of hypertension in the offspring.

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.

PKC-δ isozyme gene silencing restores vascular function in diabetic rat

Abstract Background: Endothelium and K+ channel functionality in smooth muscle cells (SMCs) regulates vascular function and is exposed to damage in diabetes. The regulatory enzyme protein kinase C (PKC) is known to play a key role in vascular tone regulation in health and disease. In this study, we evaluated the effect of PKC-δ gene silencing using small interfering RNAs (siRNAs) on endothelial dysfunction and acquired potassium channelopathy in vascular SMCs in diabetes. Methods: The experimental design comprised diabetes induction by streptozotocin (65 mg/kg) in rats, RNA interference, isolated aortic ring contractile recordings, whole-cell patch-clamp technique, measurements of reactive oxygen species (ROS), and real-time polymerase chain reaction technique. Animals were killed by cervical dislocation following ketamine (45 mg/kg, i.p.) and xylazine (10 mg/kg, i.p.) anesthesia administration on the third month of diabetes and on the seventh day after intravenous injection of siRNAs. Results: The aortas of diabetic rats demonstrated depressed endothelium-dependent relaxation and integral SMCs outward K+ currents as compared with those of controls. On the seventh day, PKC-δ gene silencing effectively restored K+ currents and increased the amplitude of vascular relaxation up to control levels. An increased level of PKC-δ mRNA in diabetic aortas appeared to be reduced after targeted PKC-δ gene silencing. Similarly, the level of ROS production that was increased in diabetes came back to control values after siRNAs administration. Conclusions: The silencing of PKC-δ gene expression using siRNAs led to restoration of vasodilator potential in rats with diabetes mellitus. It is likely that the siRNA technique can be a good therapeutic tool to normalize vascular function in diabetes.

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Size-dependent heterogeneity of contractile Ca2+ sensitization in rat arterial smooth muscle

Each segment along arterial vessels adapts to different circumstances, including blood pressure and sympathetic innervation. PKC and Rho-associated kinase (ROCK) Ca(2+)-sensitizing pathways leading to myosin phosphatase inhibition are critically involved in α(1)-adrenoceptor-mediated vascular smooth muscle contraction in distinctive time-dependent manners. We tested whether the amplitude and time course of each pathway varies dynamically between arterial segments. Using pharmacological approaches, we determined the time-dependent roles of Ca(2+) release, Ca(2+) influx, PKC and ROCK in α(1)-agonist-induced contraction and phosphorylation of key proteins in denuded rat small mesenteric artery, midsized caudal artery and thoracic aorta. SR Ca(2+) release and voltage-dependent Ca(2+) influx were essential for the initial rising and late sustained phases, respectively, of phenylephrine-induced contraction, regardless of arterial size. In small mesenteric arteries, α(1A)-subtype-specific antagonists and inhibitors of PKC, but not ROCK, markedly reduced the initial and late phases of contraction in a non-additive manner and suppressed phosphorylation of myosin light chain (MLC) and CPI-17, but not myosin targeting subunit of myosin light chain phosphatase (MYPT1). In aorta, an α(1D)-specific antagonist reduced both the initial and late phases of contraction with a significant decrease in MLC but not CPI-17 or MYPT1 phosphorylation. ROCK inhibitors, but not PKC inhibitors, suppressed the sustained phase of contraction with a decrease in MLC and MYPT1 phosphorylation in the aorta. The effect of ROCK inhibitors was additive with the α(1D)-antagonist. The results for midsized arteries were intermediate. Thus, the PKC-CPI-17 Ca(2+)-sensitizing pathway, which is dependent on PKC subtype and a Ca(2+)-handling mechanism, and is downstream of α(1A) receptors, plays a major role in α(1)-agonist-induced contraction of small resistance arteries in the splanchnic vascular beds. The effect of PKC and ROCK increases and decreases, respectively, with decreasing arterial size.

Regulation of the ATP-sensitive potassium channel subunit, Kir6.2, by a Ca2+-dependent protein kinase C

The activity of ATP-sensitive potassium (K(ATP)) channels is governed by the concentration of intracellular ATP and ADP and is thus responsive to the metabolic status of the cell. Phosphorylation of K(ATP) channels by protein kinase A (PKA) or protein kinase C (PKC) results in the modulation of channel activity and is particularly important in regulating smooth muscle tone. At the molecular level the smooth muscle channel is composed of a sulfonylurea subunit (SUR2B) and a pore-forming subunit Kir6.1 and/or Kir6.2. Previously, Kir6.1/SUR2B channels have been shown to be inhibited by PKC, and Kir6.2/SUR2B channels have been shown to be activated or have no response to PKC. In this study we have examined the modulation of channel complexes formed of the inward rectifier subunit, Kir6.2, and the sulfonylurea subunit, SUR2B. Using a combination of biochemical and electrophysiological techniques we show that this complex can be inhibited by protein kinase C in a Ca(2+)-dependent manner and that this inhibition is likely to be as a result of internalization. We identify a residue in the distal C terminus of Kir6.2 (Ser-372) whose phosphorylation leads to down-regulation of the channel complex. This inhibitory effect is distinct from activation which is seen with low levels of channel activity.

Effect of ghrelin on protein kinase C-ε and protein kinase C-δ gene expression in the pulmonary arterial smooth muscles of chronic hypoxic rats

INTRODUCTION

Protein kinase C (PKC), can be activated in pulmonary arterial smooth muscle cells during hypoxia, leading to hypoxic pulmonary vasoconstriction (HPV). Studies are going on to detect the strict PKC isoform involved in the phenomenon. It has been shown that ghrelin, a 28-amino-acid peptide, may protect lungs from HPV side effects, to some extent. The aim of study was to evaluate the effect of exogenous ghrelin on PKC-ε and PKC-δ gene expression during chronic hypoxia.

MATERIAL AND METHODS

Twenty-four adult male Wistar rats were divided randomly in 3 groups. Hypoxic rats with saline or ghrelin treatment were placed in a normobaric hypoxic chamber for 2 weeks. Controls remained in room air. PKC-ε and PKC-δ gene expression was measured by real-time RT-PCR.

RESULTS

Morphometric analysis showed that ghrelin reversed the hypoxia induced pulmonary artery wall thickness. In hypoxic animals, there was a 2- and 4-fold increment in PKC-ε and PKC- δ gene expression, respectively. Ghrelin treatment reduced the overexpression of PKC-ε and PKC-δ to control animals' value.

CONCLUSION

Ghrelin by decreasing the expression of PKC-ε and PKC-δ in hypoxic animals reduces the HPV. Although more studies are needed, it could be an honest deduction that ghrelin affects HPV in a multifunctional manner and might be used as a therapeutic agent in the future.

Involvement of protein kinase C-CPI-17 in androgen modulation of angiotensin II-renal vasoconstriction

AIMS

Previous studies suggested that androgens augmented renal vascular responses to angiotensin II (Ang II). The protein kinase C (PKC)-CPI-17 pathway is involved in vascular constriction. We tested the hypothesis that this pathway may contribute to androgenic amplification of Ang II-renal vasoconstriction in the New Zealand genetically hypertensive (NZGH) rat.

METHODS AND RESULTS

NZGH underwent sham operation, castration, or castration with testosterone replacement at 5 weeks of age. When the rats were 16-17 weeks of age, mean arterial pressure (MAP) and renal vascular resistance (RVR) responses to intravenous Ang II infusion (20, 40, and 80 ng/kg/min) were recorded before and after treatment with a PKC inhibitor, chelerythrine. mRNA expression of PKC isoforms and CPI-17 protein expression were analysed in renal cortex. MAP and RVR responses to Ang II were enhanced in androgen-replete NZGH. The Ang II-induced increase in RVR was significantly lower in castrated NZGH (ranged from 100 +/- 8% to 161 +/- 9% of baseline) than in sham-operated NZGH (ranged between 123 +/- 3% and 237 +/- 19% of baseline). Testosterone treatment restored RVR responses to Ang II in castrated rats. Chelerythrine treatment markedly reduced the MAP and RVR responses to Ang II in each group and attenuated the differential MAP and RVR responses to Ang II amongst the three groups. PKCdelta and PKCepsilon mRNA levels were significantly reduced by castration and increased by testosterone treatment. In contrast, no significant differences in protein expression were detected for these PKC isoforms. Castration decreased while testosterone treatment increased CPI-17 and phospho-CPI-17 expression.

CONCLUSION

Collectively, these results suggest that androgens modulate renal vascular responses to Ang II in part via an effect on the PKC-CPI-17 signalling pathway.

Endothelin-I and angiotensin II inhibit arterial voltage-gated K+ channels through different protein kinase C isoenzymes

AIMS

Voltage-gated K+ (Kv) channels of arterial smooth muscle (ASM) modulate arterial tone and are inhibited by vasoconstrictors through protein kinase C (PKC). We aimed to determine whether endothelin-1 (ET-1) and angiotensin II (AngII), which cause similar inhibition of Kv, use the same signalling pathway and PKC isoenzyme to exert their effects on Kv and to compare the involvement of PKC isoenzymes in contractile responses to these agents.

METHODS AND RESULTS

Kv currents recorded using the patch clamp technique with freshly isolated rat mesenteric ASM cells were inhibited by ET-1 or AngII. Inclusion of a PKCepsilon inhibitor peptide in the intracellular solution substantially reduced inhibition by AngII, but did not affect that by ET-1. Kv inhibition by ET-1 was reduced by the conventional PKC inhibitor Gö 6976 but not by the PKCbeta inhibitor LY333531. Selective peptide inhibitors of PKCalpha and PKCepsilon were linked to a Tat carrier peptide to make them membrane permeable and used to show that inhibition of PKCalpha prevented ET-1 inhibition of Kv current, but did not affect that by AngII. In contrast, inhibition of PKCepsilon prevented Kv inhibition by AngII but not by ET-1. The Tat-linked inhibitor peptides were also used to investigate the involvement of PKCalpha and PKCepsilon in the contractile responses of mesenteric arterial rings, showing that ET-1 contractions were substantially reduced by inhibition of PKCalpha, but unaffected by inhibition of PKCepsilon. AngII contractions were unaffected by inhibition of PKCalpha but substantially reduced by inhibition of PKCepsilon.

CONCLUSION

ET-1 inhibits Kv channels of mesenteric ASM through activation of PKCalpha, while AngII does so through PKCepsilon. This implies that ET-1 and AngII target Kv channels of ASM through different pathways of PKC-interacting proteins, so each vasoconstrictor enables its distinct PKC isoenzyme to interact functionally with the Kv channel.

Role of protein kinase C in 15-HETE-induced hypoxic pulmonary vasoconstriction

The aim of the present study was to investigate the roles of protein kinase C (PKC) signal transduction pathway in the 15-hydroxyeicosatetraenoic acid (15-HETE)-induced down-regulation expression of K(V) 1.5, K(V) 2.1 and K(V) 3.4, and pulmonary vasoconstriction under hypoxia. Tension measurements on rat pulmonary artery (PA) rings, Western blots, semi-quantitative PCR and whole-cell patch-clamp technique were employed to investigate the effects of 15-HETE on PKC and K(V) channels. Hypericin (6.8 micromol/L), a PKC inhibitor, significantly attenuated the constriction of PA rings to 15-HETE under hypoxia. The down-regulation of K(V) 1.5, K(V) 2.1 and K(V) 3.4 channel expression and inhibition of whole-cell K currents (I(K)(V)) induced by 15-HETE were rescued and restored, respectively, by hypericin. These studies indicate that the PKC signal transduction pathway is involved in 15-HETE-induced rat pulmonary vasoconstriction under hypoxia. 15-HETE suppresses the expression of K(V) 1.5, K(V) 2.1 and K(V) 3.4 channels and inhibits I(K)(V) through the PKC signaling pathway in pulmonary arterial smooth muscle cells.

Differential [Ca2+]i signaling of vasoconstriction in mesenteric microvessels of normal and reduced uterine perfusion pregnant rats

Vascular resistance and blood pressure (BP) are reduced during late normal pregnancy (Norm-Preg). In contrast, studies in human preeclampsia and in animal models of hypertension in pregnancy (HTN-Preg) have suggested that localized reduction in uterine perfusion pressure (RUPP) in late pregnancy is associated with increased systemic vascular resistance and BP; however, the vascular mechanisms involved are unclear. Because Ca2+ is a major determinant of vascular contraction, we hypothesized that the intracellular free calcium concentration ([Ca2+]i) signaling of vasoconstriction is differentially regulated in systemic microvessels during normal and RUPP in late pregnancy. Pressurized mesenteric microvessels from Norm-Preg and RUPP rats were loaded with fura 2 in preparation for simultaneous measurement of diameter and [Ca2+]i (presented as fura 2 340/380 ratio). Basal [Ca2+]i was lower in RUPP (0.73 +/- 0.03) compared with Norm-Preg rats (0.82 +/- 0.03). Membrane depolarization by 96 mM KCl, phenylephrine (Phe, 10(-5) M), angiotensin II (ANG II, 10(-7) M), or endothelin-1 (ET-1, 10(-7) M) caused an initial peak followed by maintained vasoconstriction and [Ca2+]i. KCl caused similar peak vasoconstriction and [Ca2+]i in Norm-Preg (45.5 +/- 3.3 and 0.89 +/- 0.02%) and RUPP rats (46.3 +/- 2.1 and 0.87 +/- 0.01%). Maximum vasoconstriction to Phe, ANG II, and ET-1 was not significantly different between Norm-Preg (28.6 +/- 4.8, 32.5 +/- 6.3, and 40 +/- 4.6%, respectively) and RUPP rats (27.8 +/- 5.9, 34.4 +/- 4.3, and 38.8 +/- 4.1%, respectively). In contrast, the initial Phe-, ANG II-, and ET-1-induced 340/380 ratio ([Ca2+]i) was reduced in RUPP (0.83 +/- 0.02, 0.82 +/- 0.02, and 0.83 +/- 0.03, respectively) compared with Norm-Preg rats (0.95 +/- 0.04, 0.93 +/- 0.01, and 0.92 +/- 0.02, respectively). Also, the [Ca2+]i-vasoconstriction relationship was similar in KCl-treated but shifted to the left in Phe-, ANG II-, and ET-1-treated microvessels of RUPP compared with Norm-Preg rats. The lower agonist-induced [Ca2+]i signal of vasoconstriction and the leftward shift in the [Ca2+]i-vasoconstriction relationship in microvessels of RUPP compared with Norm-Preg rats suggest activation of [Ca2+]i sensitization pathway(s). The similarity in vasoconstriction in RUPP and Norm-Preg rats suggests that such a [Ca2+]i sensitization pathway(s) may also provide a feedback effect on Ca2+ mobilization/homeostatic mechanisms to protect against excessive vasoconstriction in systemic microvessels during RUPP in late pregnancy.

Visualizing the temporal effects of vasoconstrictors on PKC translocation and Ca2+ signaling in single resistance arterial smooth muscle cells

Arterial smooth muscle (ASM) contraction plays a critical role in regulating blood distribution and blood pressure. Vasoconstrictors activate cell surface receptors to initiate signaling cascades involving increased intracellular Ca(2+) concentration ([Ca(2+)](i)) and recruitment of protein kinase C (PKC), leading to ASM contraction, though the PKC isoenzymes involved vary between different vasoconstrictors and their actions. Here, we have used confocal microscopy of enhanced green fluorescence protein (eGFP)-labeled PKC isoenzymes to visualize PKC translocation in primary rat mesenteric ASM cells in response to physiological vasoconstrictors, with simultaneous imaging of Ca(2+) signaling. Endothelin-1, angiotensin II, and uridine triphosphate all caused translocation of each of the PKC isoenzymes alpha, delta, and epsilon; however, the kinetics of translocation varied between agonists and PKC isoenzymes. Translocation of eGFP-PKCalpha mirrored the rise in [Ca(2+)](i), while that of eGFP-PKCdelta or -epsilon occurred more slowly. Endothelin-induced translocation of eGFP-PKCepsilon was often sustained for several minutes, while responses to angiotensin II were always transient. In addition, preventing [Ca(2+)](i) increases using 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra-(acetoxymethyl) ester prevented eGFP-PKCalpha translocation, while eGFP-PKCdelta translocated more rapidly. Our results suggest that PKC isoenzyme specificity of vasoconstrictor actions occurs downstream of PKC recruitment and demonstrate the varied kinetics and complex interplay between Ca(2+) and PKC responses to different vasoconstrictors in ASM.

The Mechanism Behind the Inhibitory Effect of Isoflurane on Angiotensin II-Induced Vascular Contraction Is Different from That of Sevoflurane

BACKGROUND

Angiotensin II (Ang II)-induced vascular contraction is mediated both by a Ca(2+)-mediated signaling pathway and a Ca(2+) sensitization mechanism. We recently demonstrated that sevoflurane inhibits the contractile response to Ang II, mainly by inhibiting protein kinase C (PKC) phosphorylation that regulates myofilament Ca(2+) sensitivity, without significant alteration of intracellular Ca(2+) concentration ([Ca(2+)](i)) in rat aortic smooth muscle. The current study was designed to determine the mechanisms by which isoflurane inhibits Ang II-induced contraction of rat aortic smooth muscle.

METHODS

The effects of isoflurane on vasoconstriction, increase in [Ca(2+)](i), and phosphorylation of PKC in response to Ang II (10(-7) M) were investigated, using an isometric force transducer, a fluorometer, and Western blotting, respectively.

RESULTS

Ang II elicited a transient contraction of rat aortic smooth muscle that was associated with an increase in [Ca(2+)](i) and PKC phosphorylation. Isoflurane (1.2%-3.5%) inhibited Ang II-induced contraction of rat aortic smooth muscle in a concentration-dependent manner (P < 0.05 at 1.2%, P < 0.01 at 2.3% and 3.5% isoflurane, n = 6). Isoflurane also inhibited elevation of [Ca(2+)](i) in response to Ang II (P < 0.01 at 2.3% and 3.5% isoflurane, n = 6), but failed to affect Ang II-induced phosphorylation of PKC at concentrations up to 3.5% (n = 7).

CONCLUSION

These results suggest that, unlike sevoflurane, the inhibitory effect of isoflurane on Ang II-induced contraction is mainly mediated by attenuation of the Ca(2+)-mediated signaling pathway.

Differential expression of PKC isoforms in developing zebrafish

Protein kinase C isozymes are a biologically diverse group of enzymes known to be involved in a wide variety of cellular processes. They fall into three families (conventional, novel and atypical) depending upon their mode of activation. Several classes of zebrafish neurons have been shown to express PKCalpha during development, but the expression of other isoforms remains unknown. In this study we performed immunohistochemistry to determine if zebrafish express various isoforms of PKC. We used antibodies to test for the presence of enzymes that are thought to be preferentially expressed in the nervous system (PKCgamma, betaII, delta, epsilon, theta and zeta). Here, we show that PKCgamma, epsilon, theta and zeta are expressed in the zebrafish CNS. Anti-PKCgamma labels Rohon-Beard sensory neurons and Mauthner cells. PKCepsilon and zeta staining is widespread in the CNS, and PKCtheta and betaII are expressed in skeletal muscle, especially at intersegmental boundaries. Immunoblot experiments confirm the specificity of the antibodies in zebrafish and indicate that the fish isoforms of PKCgamma, betaII, epsilon and zeta are similar to the mammalian isoforms. Interestingly, PKCtheta appears to be similar to PKCthetaII, which, to date, has been found exclusively in mouse testis, but not in the mammalian CNS. Overall, our findings indicate that several different PKC isoforms are expressed in zebrafish, and that Rohon-Beard, Mauthner cells and muscle fibers preferentially express some isoforms over others.

Molecular and structural basis of portal hypertension

Portal hypertension is a complication of diseases that obstruct portal blood flow, such as cirrhosis or portal vein thrombosis. In these diseases, increased vascular resistance to portal blood flow is the primary mechanism that increases portal pressure. In cirrhosis, increased intrahepatic vascular resistance is a result of both intrahepatic vasoconstriction and surrounding mechanical factors including collagen deposition and regenerative nodules. This article summarizes recent progress in the understanding of molecular mechanisms underlying the portal hypertension-associated arterial alterations in splanchnic systemic territories and those involved in the development of portal-systemic collateral circulation.

Angiotensin II inhibits inward rectifier K+ channels in rabbit coronary arterial smooth muscle cells through protein kinase Calpha

We investigated the effects of the vasoconstrictor angiotensin (Ang) II on the whole cell inward rectifier K(+) (Kir) current enzymatically isolated from small-diameter (<100 microm) coronary arterial smooth muscle cells (CASMCs). Ang II inhibited the Kir current in a dose-dependent manner (half inhibition value: 154 nM). Pretreatment with phospholipase C inhibitor and protein kinase C (PKC) inhibitors prevented the Ang II-induced inhibition of the Kir current. The PKC activator reduced the Kir currents. The inhibitory effect of Ang II was reduced by intracellular and extracellular Ca(2+) free condition and by Gö6976, which inhibits Ca(2+)-dependent PKC isoforms alpha and beta. However, the inhibitory effect of Ang II was unaffected by a peptide that selectively inhibits the translocation of the epsilon isoform of PKC. Western blot analysis confirmed that PKCalpha, and not PKCbeta, was expressed in small-diameter CASMCs. The Ang II type 1 (AT(1))-receptor antagonist CV-11974 prevented the Ang II-induced inhibition of the Kir current. From these results, we conclude that Ang II inhibits Kir channels through AT(1) receptors by the activation of PKCalpha.

Effect of des-aspartate-angiotensin I on the actions of angiotensin II in the isolated renal and mesenteric vasculature of hypertensive and STZ-induced diabetic rats

The present study investigated the action of des-aspartate-angiotensin I (DAA-I) on the pressor action of angiotensin II in the renal and mesenteric vasculature of WKY, SHR and streptozotocin (STZ)-induced diabetic rats. Angiotensin II-induced a dose-dependent pressor response in the renal vasculature. Compared to the WKY, the pressor response was enhanced in the SHR and reduced in the STZ-induced diabetic rat. DAA-I attenuated the angiotensin II pressor action in renal vasculature of WKY and SHR. The attenuation was observed for DAA-I concentration as low as 10(-18) M and was more prominent in SHR. However, the ability of DAA-I to reduce angiotensin II response was lost in the STZ-induced diabetic kidney. Instead, enhancement of angiotensin II pressor response was seen at the lower doses of the octapeptide. The effect of DAA-I was not inhibited by PD123319, an AT2 receptor antagonist, and indomethacin, a cyclo-oxygenase inhibitor in both WKY and SHR, indicating that its action was not mediated by angiotensin AT2 receptor and prostaglandins. The pressor responses to angiotensin II in mesenteric vascular bed were also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses were significantly smaller in SHR but no significant difference was observed between STZ-induced diabetic and WKY rat. Similarly, PD123319 and indomethacin had no effect on the action of DAA-I. The findings reiterate a regulatory role for DAA-I in vascular bed of the kidney and mesentery. By being active at circulating level, DAA-I subserves a physiological role. This function appears to be present in animals with diseased state of hypertension and diabetes. It is likely that DAA-I functions are modified to accommodate the ongoing vascular remodeling.

Identification of the linker histone H1 as a protein kinase Cepsilon-binding protein in vascular smooth muscle

A variety of anchoring proteins target specific protein kinase C (PKC) isoenzymes to particular subcellular locations or multimeric signaling complexes, thereby achieving a high degree of substrate specificity by localizing the kinase in proximity to specific substrates. PKCepsilon is widely expressed in smooth muscle tissues, but little is known about its targeting and substrate specificity. We have used a Far-Western (overlay) approach to identify PKCepsilon-binding proteins in vascular smooth muscle of the rat aorta. Proteins of approximately 32 and 34 kDa in the Triton-insoluble fraction were found to bind PKCepsilon in a phospholipid/diacylglycerol-dependent manner. Although of similar molecular weight to RACK-1, a known PKCepsilon-binding protein, these proteins were separated from RACK-1 by SDS-PAGE and differential NaCl extraction and were not recognized by an antibody to RACK-1. The PKCepsilon-binding proteins were further purified from the Triton-insoluble fraction and identified by de novo sequencing of selected tryptic peptides by tandem mass spectrometry as variants of the linker histone H1. Their identity was confirmed by Western blotting with anti-histone H1 and the demonstration that purified histone H1 binds PKCepsilon in the presence of phospholipid and diacylglycerol but absence of Ca(2+). The interaction of PKCepsilon with histone H1 was specific since no interaction was observed with histones H2A, H2S or H3S. Bound PKCepsilon phosphorylated histone H1 in a phospholipid/diacylglycerol-dependent but Ca(2+)-independent manner. Ca(2+)-dependent PKC was also shown to interact with histone H1 but not other histones. These results suggest that histone H1 is both an anchoring protein and a substrate for activated PKCepsilon and other PKC isoenzymes and likely serves to localize activated PKCs that translocate to the nucleus in the vicinity of specific nuclear substrates including histone H1 itself. Since PKC isoenzymes have been implicated in regulation of gene expression, stable interaction with histone H1 may be an important step in this process.

Alpha1-adrenergic signaling mechanisms in contraction of resistance arteries

Our goal in this review is to provide a comprehensive, integrated view of the numerous signaling pathways that are activated by alpha(1)-adrenoceptors and control actin-myosin interactions (i.e., crossbridge cycling and force generation) in mammalian arterial smooth muscle. These signaling pathways may be categorized broadly as leading either to thick (myosin) filament regulation or to thin (actin) filament regulation. Thick filament regulation encompasses both "Ca(2+) activation" and "Ca(2+)-sensitization" as it involves both activation of myosin light chain kinase (MLCK) by Ca(2+)-calmodulin and regulation of myosin light chain phosphatase (MLCP) activity. With respect to Ca(2+) activation, adrenergically induced Ca(2+) transients in individual smooth muscle cells of intact arteries are now being shown by high resolution imaging to be sarcoplasmic reticulum-dependent asynchronous propagating Ca(2+) waves. These waves differ from the spatially uniform increases in [Ca(2+)] previously assumed. Similarly, imaging during adrenergic activation has revealed the dynamic translocation, to membranes and other subcellular sites, of protein kinases (e.g., Ca(2+)-activated protein kinases, PKCs) that are involved in regulation of MLCP and thus in "Ca(2+) sensitization" of contraction. Thin filament regulation includes the possible disinhibition of actin-myosin interactions by phosphorylation of CaD, possibly by mitogen-activated protein (MAP) kinases that are also translocated during adrenergic activation. An hypothesis for the mechanisms of adrenergic activation of small arteries is advanced. This involves asynchronous Ca(2+) waves in individual SMC, synchronous Ca(2+) oscillations (at high levels of adrenergic activation), Ca(2+) sparks, "Ca(2+)-sensitization" by PKC and Rho-associated kinase (ROK), and thin filament mechanisms.

PKC activates BKCa channels in rat pulmonary arterial smooth muscle via cGMP-dependent protein kinase

Normally, signaling mechanisms that activate large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channels in pulmonary vascular smooth muscle cause pulmonary vasodilatation. BK(Ca)-channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (decrease in the opening probability) of the BK(Ca) channel has been implicated in the development of pulmonary vasoconstriction. Protein kinase C (PKC) causes pulmonary vasoconstriction, but little is known about the effect of PKC on BK(Ca)-channel activity in pulmonary vascular smooth muscle. Accordingly, studies were done to determine the effect of PKC on BK(Ca)-channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMCs) of the Sprague-Dawley rat. The PKC activators phorbol myristate acetate (PMA) and thymeleatoxin opened BK(Ca) channels in single Sprague-Dawley rat PASMC. The activator response to both PMA and thymeleatoxin on BK(Ca)-channel activity was blocked by Gö-6983, which selectively blocks PKC-alpha, -delta, -gamma, and -zeta, and by rottlerin, which selectively inhibits PKC-delta. In addition, the specific cyclic GMP-dependent protein kinase antagonist KT-5823 blocked the responses to PMA and thymelatoxin, whereas the specific cyclic AMP-dependent protein kinase blocker KT-5720 had no effect. In isolated pulmonary arterial vessels, both PMA and forskolin caused vasodilatation, which was inhibited by KT-5823, Gö-6983, or the BK(Ca)-channel blocker tetraethylammonium. The results of this study indicate that activation of specific PKC isozymes increases BK(Ca)-channel activity in Sprague-Dawley rat PASMC via cyclic GMP-dependent protein kinase, which suggests a unique signaling mechanism for vasodilatation.

Protein kinase C inhibits BKCa channel activity in pulmonary arterial smooth muscle

Signaling mechanisms that elevate cyclic AMP (cAMP) activate large-conductance, calcium- and voltage-activated potassium (BKCa) channels in pulmonary vascular smooth muscle and cause pulmonary vasodilatation. BKCa channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BKCa channel has been implicated in the development of pulmonary vasoconstriction. Protein kinase C (PKC) causes pulmonary vasoconstriction, but little is known about the effect of PKC on BKCa channel activity. Accordingly, studies were done to determine the effect of PKC activation on cAMP-induced BKCa channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMC) of the fawn-hooded rat (FHR), a recognized animal model of pulmonary hypertension. Forskolin (10 microM), a stimulator of adenylate cyclase and an activator of cAMP, opened BKCa channels in single FHR PASMC, which were blocked by the PKC activators phorbol 12-myristate 13-acetate (100 nM) and thymeleatoxin (100 nM). The inhibitory response by thymeleatoxin on forskolin-induced BKCa channel activity was blocked by Gö-6983, which selectively blocks the alpha, beta, delta, gamma, and zeta PKC isozymes, and Gö-6976, which selectively inhibits PKC-alpha, PKC-beta, and PKC-mu, but not by rottlerin, which selectively inhibits PKC-delta. Collectively, these results indicate that activation of specific PKC isozymes inhibits cAMP-induced activation of the BKCa channel in pulmonary arterial smooth muscle, which suggests a unique signaling pathway to modulate BKCa channels and subsequently cAMP-induced pulmonary vasodilatation.

Modulation of protein kinase C (PKC)-mediated contraction and the possible role of PKC epsilon in rat mesenteric arteries

he involvement of protein kinase C (PKC) in isometric tension development of rat mesenteric arteries was investigated. Non-selective inhibition of PKC and selective inhibition of the epsilon isoform were performed using the PKC inhibitor, chelerythrine, and non-viral gene-transfer of a kinase inactive mutant of PKCepsilon (PKCepsilon-KN), respectively. Chelerythrine (2.5 or 5.0 microM) significantly and equally attenuated phenylephrine-induced but not potassium-induced contractions. Higher concentrations of chelerythrine (10 microM) caused the vessels to lose responsiveness to both phenylephrine and potassium chloride. Transfection of blood vessels with epsilon-KN also resulted in significant attenuation of contractile responses to phenylephrine. Potassium chloride-induced responses were not altered in transfected arteries. In a separate group of vessels, the relationship between [Ca2+]i and isometric tension was evaluated. These studies suggested that calcium sensitivity of the contractile apparatus was decreased in vessels when PKC-epsilon activity was compromised. The results of the study suggest that PKC-epsilon can modulate phenylephrine-induced contraction in mesenteric arteries via calcium-independent pathways.

Phorbol ester-induced contractility and Ca2+ influx in human cultured prostatic stromal cells

In this study, we investigated the effects of protein kinase C (PKC)-activating phorbol esters upon Ca(2+) influx and contractility in human cultured prostatic stromal cells. Tissue obtained from patients undergoing transurethral resection of the prostate was used to generate explant cultures of prostatic stromal cells. These cells expressed detectable levels of PKCalpha, delta, gamma, lambda, and zeta, but not epsilon, iota, mu, or theta; isoforms and responded to both phorbol 12,13-diacetate (PDA) and 12-deoxyphorbol 13-tetradecanoate (DPT) with concentration-dependent contractions (pEC50+/-SEM 7.07+/-0.41 and 6.39+/-0.27, respectively). The L-type Ca2+ channel blocker nifedipine (3 microM), and the PKC inhibitors Gö 6976, Gö 6983 (both 100 nM), myristoylated PKC inhibitor 19-27 (20 microM) and bisindolylmaleimide (1 microM) all abolished PDA-stimulated (1 microM) contractions. Neither PDA nor DPT (at 1 microM) caused translocation of any PKC isoform from the cytosolic to the particulate fraction. Nifedipine (3 microM), myristoylated PKC inhibitor 19-27 (20 microM), and bisindolylmaleimide (1 microM) inhibited PDA-stimulated Ca2+ influx into FURA-2 loaded cells. This study indicates that human cultured prostatic stromal cells respond to phorbol esters with contractions that are dependent upon the influx of Ca2+ through L-type Ca2+ channels and that this effect may be independent of the translocation of PKC from cytosolic to particulate fractions.

Phosphorylation of kinase-related protein (telokin) in tonic and phasic smooth muscles

KRP (telokin), an independently expressed C-terminal myosin-binding domain of smooth muscle myosin light chain kinase (MLCK), has been reported to have two related functions. First, KRP stabilizes myosin filaments (Shirinsky et al., 1993, J. Biol. Chem. 268, 16578-16583) in the presence of ATP. Secondly, KRP can modulate the level of myosin light chain phosphorylation. In this latter role, multiple mechanisms have been suggested. One hypothesis is that light chain phosphorylation is diminished by the direct competition of KRP and MLCK for myosin, resulting in a loss of contraction. Alternatively, KRP, through an unidentified mechanism, accelerates myosin light chain dephosphorylation in a manner possibly enhanced by KRP phosphorylation. Here, we demonstrate that KRP is a major phosphoprotein in smooth muscle, and use a comparative approach to investigate how its phosphorylation correlates with sustained contraction and forskolin-induced relaxation. Forskolin relaxation of precontracted artery strips caused little increase in KRP phosphorylation, while treatment with phorbol ester increased the level of KRP phosphorylation without a subsequent change in contractility. Although phorbol ester does not induce contraction of phasic tissues, the level of KRP phosphorylation is increased. Phosphopeptide maps of KRP from both tissues revealed multiple sites of phosphorylation within the N-terminal region of KRP. Phosphopeptide maps of KRP from gizzard were more complex than those for KRP from artery consistent with heterogeneity at the amino terminus and/or additional sites. We discovered through analysis of KRP phosphorylation in vitro that Ser12, Ser15 and Ser15 are phosphorylated by cAMP-dependent protein kinase, mitogen-activated protein (MAP) kinase and glycogen synthase kinase 3 (GSK3), respectively. Phosphorylation by GSK3 was dependent upon prephosphorylation by MAP kinase. This appears to be the first report of conditional or hierarchical phosphorylation of KRP. Peptides consistent with such multiple phosphorylations were found on the in vivo phosphopeptide maps of avian KRP. Collectively, the available data indicate that there is a complex relationship between the in vivo phosphorylation states of KRP and its effects on relaxation in smooth muscle.

Sildenafil and T-1032, phosphodiesterase type 5 inhibitors, showed a different vasorelaxant property in the isolated rat aorta

The vasorelaxant effects of sildenafil and T-1032 [methyl-2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridinylmethoxy)-4-(3,4,5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate], two phosphodiesterase type 5 inhibitors, were examined in the isolated rat aorta. Sildenafil and T-1032, both of which have almost the same potency and selectivity regarding phosphodiesterase type 5 inhibitory activity, produced a similar, moderate, relaxation at 10(-10) to 10(-7) M (sildenafil: 66.8 +/- 13.7%; T-1032: 77.9 +/- 10.8% at 10(-7) M). However, sildenafil, but not T-1032, produced further relaxation at the higher concentrations (sildenafil: 102.0 +/- 0.6%; T-1032: 81.0 +/- 7.2% at 10(-4) M, P < 0.05). Sildenafil also produced a more potent relaxation than did T-1032 at the high concentrations (10(-5) and 10(-4) M) in endothelium-denuded aortic rings and in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor (3 x 10(-4) M). Moreover, the high concentrations of sildenafil, but not of T-1032, caused a rightward shift of the concentration-response curve for calcium chloride in K(+)-depolarized endothelium-denuded preparations. In the ligand binding assay for the L-type Ca(2+) channels, the affinities of sildenafil at 10(-5) M for binding sites of nitrendipine and (--)-desmethoxyverapamil [(--)- D888] (35.2 +/- 3.3% and 35.8 +/- 1.9%, respectively) were higher than those of T-1032 (11.8 +/- 4.0% and -13.1 +/- 1.3%, respectively, P < 0.05). Regarding cyclic nucleotide levels, both phosphodiesterase type 5 inhibitors increased cGMP levels at 10(-6) M. However, sildenafil, but not T-1032, further increased cGMP levels at the higher concentrations (sildenafil: 15.7 +/- 2.7 pmol/mg protein; T-1032: 5.6 +/- 0.6 pmol/mg protein at 10(-4) M, P < 0.05). These results suggested that high concentrations of sildenafil had additional vasorelaxant properties through mechanisms other than phosphodiesterase type 5 inhibition. Sildenafil-induced relaxation appears to be due to inhibition of the external Ca(2+)-dependent cascade for contraction and/or to an increase in cGMP levels. In contrast, T-1032 only showed a vasorelaxant property due to phosphodiesterase type 5 inhibition. In conclusion, T-1032 appears to be a specific phosphodiesterase type 5 inhibitor compared with sildenafil and a useful compound to examine the physiological function of phosphodiesterase type 5.

Coupling strength between localized Ca(2+) transients and K(+) channels is regulated by protein kinase C

Localized Ca(2+) transients resulting from inositol trisphosphate (IP(3))-dependent Ca(2+) release couple to spontaneous transient outward currents (STOCs) in murine colonic myocytes. Confocal microscopy and whole cell patch-clamp techniques were used to investigate coupling between localized Ca(2+) transients and STOCs. Colonic myocytes were loaded with fluo 3. Reduction in external Ca(2+) ([Ca(2+)](o)) reduced localized Ca(2+) transients but increased STOC amplitude and frequency. Simultaneous recordings of Ca(2+) transients and STOCs showed increased coupling strength between Ca(2+) transients and STOCs when [Ca(2+)](o) was reduced. Gd(3+) (10 microM) did not affect Ca(2+) transients but increased STOC amplitude and frequency. Similarly, an inhibitor of Ca(2+) influx, 1-2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1H-imidazole (SKF-96365), increased STOC amplitude and frequency. A protein kinase C (PKC) inhibitor, GF-109203X, also increased the amplitude and frequency of STOCs but had no effect on Ca(2+) transients. Phorbol 12-myristate 13-acetate (1 microM) reduced STOC amplitude and frequency but did not affect Ca(2+) transients. 4alpha-Phorbol (1 microM) had no effect on STOCs or Ca(2+) transients. Single channel studies indicated that large-conductance Ca(2+)-activated K(+) (BK) channels were inhibited by a Ca(2+)-dependent PKC. In summary 1) Ca(2+) release from IP(3) receptor-operated stores activates Ca(2+)-activated K(+) channels; 2) Ca(2+) influx through nonselective cation channels facilitates activation of PKC; and 3) PKC reduces the Ca(2+) sensitivity of BK channels, reducing the coupling strength between localized Ca(2+) transients and BK channels.

Role of protein kinase C in myogenic calcium-contraction coupling of rat cannulated mesenteric small arteries

1. The present study was designed to determine the role of protein kinase C (PKC) in the myogenic response of small arteries. In particular, we tested whether inhibition of PKC reverses the previously found pressure-induced elevation of contractile element calcium sensitivity. 2. Rat mesenteric small arteries were cannulated and pressurized. The internal diameter was continuously monitored with a video camera and intracellular calcium levels were measured by means of fura-2. Myogenic responses were observed when the pressure was raised stepwise from 20 to 60 and then to 100 mmHg in physiological saline solution and during application of phenylephrine (0.1 or 1 micromol/L) or potassium (36 mmol/L). 3. The PKC inhibitors H-7 (20 micromol/L), staurosporine (100 nmol/L) and calphostin C (10 nmol/L) all completely abolished the myogenic response. Whereas staurosporine caused an ongoing reduction in intracellular calcium, pressure-induced calcium transients were not affected by either H-7 or calphostin C. In particular, the slope of the wall tension-calcium relationship remained similar in the presence of both H-7 and calphostin C, despite an upward shift of this relationship to higher calcium levels in the case of calphostin C. 4. These results show that activity of PKC isoform(s) is essential for myogenic calcium-contraction coupling.

Mechanism of action of angiotensin II in human isolated subcutaneous resistance arteries

1. Human isolated subcutaneous arteries were mounted in a myograph and isometric tension measured. In some experiments, intracellular calcium [Ca(2+)]i was also measured using fura-2. 2. Angiotensin II (100 pM - 1 microM) increased [Ca(2+)]i and tone in a concentration-dependent manner. The effects of angiotensin II (100 nM) were inhibited by an AT1-receptor antagonist, candesartan (100 pM). 3. Ryanodine (10 microM), had no effect on angiotensin II-induced responses, but removal of extracellular Ca(2+) abolished angiotensin II-induced rise in [Ca(2+)]i and tone. Inhibition of Ca(2+) entry by Ni(2+) (2 mM), also inhibited angiotensin II responses. The dihydropyridine, L-type calcium channel antagonist, amlodipine (10 microM), only partially attenuated angiotensin II responses. 4. Inhibition of protein kinase C (PKC) by chelerythrine (1 microM), or by overnight exposure to a phorbol ester (PDBu; 500 nM) had no effect on angiotensin II-induced contraction. 5. Genistein (10 microM), a tyrosine kinase inhibitor, inhibited angiotensin II-induced contraction, but did not inhibit the rise in [Ca(2+)]i, suggesting that at this concentration it affected the calcium sensitivity of the contractile apparatus. Genistein did not affect responses to norepinephrine (NE) or high potassium (KPSS). 6. A selective MEK inhibitor, PD98059 (30 microM), inhibited both the angiotensin II-induced contraction and rise in [Ca(2+)]i, but had no effect on responses to NE or KPSS. 7. AT1 activation causes Ca(2+) influx via L-type calcium channels and a dihydropyridine-insensitive route, but does not release Ca(2+) from intracellular sites. Activation of tyrosine kinase(s) and the ERK 1/2 pathway, but not classical or novel PKC, also play a role in angiotensin II-induced contraction in human subcutaneous resistance arteries.

The influence of chloroethylclonidine-induced contraction in isolated arteries of Wistar Kyoto rats: alpha1D- and alpha1A-adrenoceptors, protein kinase C, and calcium influx

BACKGROUND

It has recently been reported that chloroethylclonidine (CEC) elicited contraction in tail arteries (alpha(1A)-adrenoceptors) and aorta (alpha(1D)-adrenoceptors) from normotensive and spontaneously hypertensive rats (SHR). This study investigated the relationship between CEC-induced contraction and the role of protein kinase C (PKC) and extracellular Ca(++) influx in tail arteries and aorta from Wistar Kyoto rats (WKY).

METHODS

Time-course of CEC-induced contraction in endothelium-denuded arteries from Wistar, WKY, and SHR rats was evaluated. In WKY arteries, calphostin C (1 x 10(-6) M) and nitrendipine (1 x 10(-6) M) were used to determine the role of PKC and extracellular Ca(+1) in the contractile response to CEC, respectively.

RESULTS

Chloroethylclonidine (1 x 10(-4) M) elicited contraction in tail arteries and aorta from normotensive and hypertensive rats. Maximal response to CEC was similar in tail arteries among strains (approximately 30% of norepinephrine effect), while in aorta CEC elicited a higher contraction in WKY and SHR than in Wistar (59, 86, and 18% of norepinephrine effect, respectively). CEC-elicited maximal contractile responses were reached in 5 min in tail arteries and in 30-45 min in aorta irrespective of the rat strain, suggesting that different intracellular signaling pathways are involved in the contractile response to CEC in these arteries. In WKY tail arteries, calphostin C and nitrendipine blocked CEC-induced contraction while in aorta nitrendipine, but not calphostin C, inhibited CEC action.

CONCLUSIONS

This study confirms marked strain-dependent differences in rat aorta responsiveness to CEC and suggests a central role for PKC in response to CEC in tail arteries and for extracellular Ca(+1) influx in aorta.

Differential ANG II-induced growth activation pathways in mesenteric artery smooth muscle cells from SHR

Angiotensin II-induced growth signaling mechanisms were investigated in vascular smooth muscle cells (VSMCs) from mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). In WKY, angiotensin II significantly increased protein synthesis ([(3)H]leucine incorporation) but not DNA synthesis ([(3)H]thymidine incorporation). In SHR, angiotensin II increased protein and DNA synthesis. VSMCs from both strains expressed angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors. Losartan (an AT(1) receptor antagonist) but not PD-123319 (an AT(2) receptor antagonist) attenuated angiotensin II-stimulated protein synthesis in WKY VSMCs. In SHR, losartan and PD-123319 partially inhibited angiotensin II-induced VSMC proliferation. The mitogen-activated protein kinase or extracellular signal-regulated protein kinase (ERK) kinase inhibitor PD-98059 blocked VSMC growth responses to angiotensin II in both strains. Angiotensin II increased ERK1/2 activation more in SHR than WKY, an effect inhibited by losartan but not PD-123319. LY-294002 [a phosphatidylinositol-3 (PI3) kinase inhibitor] blocked angiotensin II-stimulated ERK1/2 activation in SHR but not in WKY, whereas bisindolylmaleimide [a protein kinase C (PKC) inhibitor] was ineffective. In conclusion, angiotensin II stimulates VSMC proliferation via AT(1) and AT(2) receptors in SHR. In WKY, angiotensin II induces VSMC hypertrophy via AT(1) receptors. ERK1/2-dependent pathways regulated by intracellular Ca(2+) but not PKC mediate these effects. In SHR VSMCs, PI3 kinase plays a role in augmented angiotensin II-induced ERK1/2 phosphorylation. These angiotensin II-mediated signaling events could contribute to vascular remodeling in SHR.

Effect of protein kinase C inhibition on hypoxic pulmonary vasoconstriction

The current study was done to test the hypothesis that protein kinase C (PKC) inhibitors prevent the increase in pulmonary vascular resistance and compliance that occurs in isolated, blood-perfused dog lungs during hypoxia. Pulmonary vascular resistances and compliances were measured with vascular occlusion techniques. Hypoxia significantly increased pulmonary arterial resistance, pulmonary venous resistance, and pulmonary capillary pressure and decreased total vascular compliance by decreasing both microvascular and large-vessel compliances. The nonspecific PKC inhibitor staurosporine (10(-7) M), the specific PKC blocker calphostin C (10(-7) M), and the specific PKC isozyme blocker Gö-6976 (10(-7) M) inhibited the effect of hypoxia on pulmonary vascular resistance and compliance. In addition, the PKC activator thymeleatoxin (THX; 10(-7) M) increased pulmonary vascular resistance and compliance in a manner similar to that in hypoxia, and the L-type voltage-dependent Ca(2+) channel blocker nifedipine (10(-6) M) inhibited the response to both THX and hypoxia. These results suggest that PKC inhibition blocks the hypoxic pressor response and that the pharmacological activation of PKC by THX mimics the hypoxic pulmonary vasoconstrictor response. In addition, L-type voltage-dependent Ca(2+) channel blockade may prevent the onset of the hypoxia- and PKC-induced vasoconstrictor response in the canine pulmonary vasculature.

Vascular smooth muscle cell signaling in cirrhosis and portal hypertension

Abnormal vascular responsiveness to ligands has been frequently observed in cirrhosis and portal hypertension, but its existence is not proven. The signaling pathways in vascular smooth muscle cells (VSMCs) have been studied only in animal models of cirrhosis and portal hypertension. Emerging evidence suggests that active relaxation, expressed as augmented content or activity of effectors within the cyclic AMP signaling pathway and suppressed content or activity of effectors in the inositol 1,4,5-trisphosphate/1,2-diacylglycerol signaling pathway, may be occurring in VSMCs of the splanchnic circulation in portal hypertension. The evidence supporting the existence of this phenomenon in the VSMCs of extrasplanchnic circulations in portal hypertension, as well as in the splanchnic circulation when chronic cellular damage is present, is very limited. The status of the other signaling pathways associated with contractile functions of the VSMCs, viz., cyclic GMP and tyrosine kinase-linked pathways, is unknown. The status of all the signaling pathways in non-contractile functions of VSMCs, such as growth and remodeling, has not been studied. As our overall understanding on the signaling pathways in VSMCs is only emerging, it is premature to implicate altered activity of the signaling pathways as the underlying basis of vascular hyporesponsiveness in cirrhosis and portal hypertension, and to extrapolate these limited observations to the human condition.

Effects of PKC isozyme inhibitors on constrictor responses in the feline pulmonary vascular bed

The effects of Gö-6976, a Ca(2+)-dependent protein kinase C (PKC) isozyme inhibitor, and rottlerin, a PKC-delta isozyme/calmodulin (CaM)-dependent kinase III inhibitor, on responses to vasopressor agents were investigated in the feline pulmonary vascular bed. Injections of angiotensin II, norepinephrine (NE), serotonin, BAY K 8644, and U-46619 into the lobar arterial constant blood flow perfusion circuit caused increases in pressure. Gö-6976 reduced responses to angiotensin II; however, it did not alter responses to serotonin, NE, or U-46619, whereas Gö-6976 enhanced BAY K 8644 responses. Rottlerin reduced responses to angiotensin II and NE, did not alter responses to serotonin or U-46619, and enhanced responses to BAY K 8644. Immunohistochemistry of feline pulmonary arterial smooth muscle cells demonstrated localization of PKC-alpha and -delta isozymes in response to phorbol 12-myristate 13-acetate and angiotensin II. Localization of PKC-alpha and -delta isozymes decreased with administration of Gö-6976 and rottlerin, respectively. These data suggest that activation of Ca(2+)-dependent PKC isozymes and Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate angiotensin II responses. These data further suggest that Ca(2+)-independent PKC-delta isozyme/CaM-dependent kinase III mediate responses to NE. A rottlerin- or Gö-6976-sensitive mechanism is not involved in mediating responses to serotonin and U-46619, but these PKC isozyme inhibitors enhanced BAY K 8644 responses in the feline pulmonary vascular bed.

Evidence for involvement of the PKC-alpha isoform in myogenic contractions of the coronary microcirculation

The role of protein kinase C (PKC) isoforms in myogenic tone of the ferret coronary microcirculation was investigated by measuring fura 2 Ca(2+) signals, PKC immunoblots, contractile responses, and confocal microscopy of PKC translocation. Phorbol ester-evoked contractions were completely abolished in the absence of extracellular Ca(2+) but involved a Ca(2+) sensitization relative to KCl contractions. Immunoblotting using isoform-specific antibodies showed the presence of PKC-alpha and -iota and traces of PKC-epsilon and -mu in the ferret coronary microcirculation. PKC-beta was not detectable. When intraluminal pressure (40 to 60 and 80 mmHg) was increased, ferret coronary arterioles showed a transient increase in fura 2 Ca(2+) signals, whereas the myogenic tone remained sustained. The increase in Ca(2+) and tone was sustained at 100 mmHg. Isolated ferret coronary arterioles were fixed and immunostained for PKC-alpha at 40 and 100 mmHg intraluminal pressure. PKC translocation was determined by confocal microscopy. Increased PKC translocation was observed when vessels were exposed to 100 mmHg relative to that at resting pressure (40 mmHg). These results suggest a link between the Ca(2+) sensitization that occurs during the myogenic contraction and activation of the alpha-isoform of PKC.

Changes in protein kinase C isoforms in association with vascular hyporeactivity in cirrhotic rat aortas

BACKGROUND & AIMS

Although protein kinase C (PKC) alterations may play a role in the abnormal reactivity of cirrhotic rat aortas, its isoforms and cellular distribution are unknown. We therefore studied the protein expression and cellular distribution of PKC isoforms and their activation in cirrhotic rat aortas.

METHODS

Endothelium-denuded aortas from control and cirrhotic rats were examined. Immunoblots were performed with PKC isoform-specific antibodies. Aortic reactivity was determined for phorbol myristate acetate and phenylephrine after PKC down-regulation.

RESULTS

PKC-alpha expression was reduced in both the cytosolic and membrane fractions in cirrhotic aortas. Trace amounts of PKC-beta were detected in cirrhotic aortas. PKC-delta was detected in the cytosolic fraction of control and cirrhotic aortas. PKC-zeta was detected in the membrane fraction in control aortas and in the cytosolic fraction in cirrhotic aortas. Phorbol myristate acetate and phenylephrine triggered translocation of PKC-alpha and PKC-delta isoforms from the cytosol to the membrane in control aortas; in cirrhotic aortas, only PKC-alpha was translocated. Aortic reactivities were reduced after PKC down-regulation. PKC-alpha and -delta activities were reduced in cirrhotic aortas.

CONCLUSIONS

These results suggest that a change in PKC isoforms may be responsible in part for the abnormal reactivity and intracellular transduction through the PKC pathway in cirrhotic rat aortas.

The role of nitric oxide in the reduction of protein kinase C-induced contractile response in aortae from rats with portal hypertension

BACKGROUND/AIMS

Protein kinase C plays a role in the regulation of vascular cell contraction but its activity may be reduced by nitric oxide. In portal hypertension, the exact mechanism by which nitric oxide induces vascular hyporeactivity to vasoconstrictors is unclear. The aim of this study was to investigate the role of the interaction of nitric oxide and protein kinase C in the vascular reactivity in isolated aortae from portal vein-stenosed rats.

METHODS/RESULTS

The contractile response to phorbol 12,13-dibutyrate, a protein kinase C activator, was significantly reduced in portal vein-stenosed aortae compared to sham-operated aortae. Preincubation with N-nitro-L-arginine or endothelium removal enhanced the response to phorbol 12,13-dibutyrate. The hyporesponsiveness to phorbol 12,13-dibutyrate in portal vein-stenosed rat aortae was only corrected after endothelium removal. The time course of contractions induced by phorbol 12,13-dibutyrate showed that the contraction was maintained for 2 h in sham-operated aortae and decreased to baseline in portal vein-stenosed rat aortae. This decrease was inhibited by N-nitro-L-arginine preincubation or endothelium removal. Protein kinase C downregulation caused a more marked reduction of phenylephrine-induced contraction in portal vein-stenosed aortae than in sham-operated aortae. The time course of total nitric oxide synthase activity in the presence of phorbol 12,13-dibutyrate showed a decrease in nitric oxide synthase activity after 30 min in both groups. Nitric oxide synthase activity remained stable for 120 min in sham-operated aortae but returned to basal level in portal vein-stenosed aortae.

CONCLUSIONS

Hyporeactivity to vasoconstrictors in portal vein-stenosed rat aortae may be due, in part, to a decrease in protein kinase C activation caused by nitric oxide overproduction.

AT(1)-signalling in vascular smooth muscle

Angiotensin II activates multiple signalling pathways in vascular smooth muscle. The precise pattern of signals and their relative importance to a particular functional response depends on both cell type and differentiation state. Although the contractile and trophic effects of Ang II are often thought of as distinct responses it is increasingly difficult to differentiate them in terms of signalling pathways. Since vasoconstriction and abnormal growth are both features of circulatory diseases such as hypertension and atherosclerosis a better understanding of the signalling pathways responsible for the vasoconstrictor and trophic actions of this peptide may help define novel therapeutic targets in cardiovascular disease.

Preconditioning of coronary artery against vasoconstriction by endothelin-1 and prostaglandin F2alpha during repeated downregulation of epsilon-protein kinase C

The cellular mechanisms of coronary vasospasm are unclear, and a role for protein kinase C (PKC) activation by the endogenous vasoconstrictors endothelin-1 (ET-1) and prostaglandin F2alpha (PGF2alpha) has been suggested. In this study, we developed a phorbol ester-induced PKC downregulation protocol to investigate the relation between the amount and activity of specific PKC isoforms in coronary arterial smooth muscle and coronary vasoconstriction by ET-1 and PGF2alpha. Isometric tension was measured in deendothelialized porcine coronary artery strips, [Ca2+]i was monitored in single coronary smooth muscle cells loaded with fura-2, and the whole tissue, cytosolic, and particulate fractions were examined for PKC activity and reactivity with isoform-specific anti-PKC antibodies using Western blot analysis. In Ca(2+)-free (2 mM EGTA) Krebs solution, ET-1 (10(-7) M), PGF2alpha (10(-5) M) and PKC activator phorbol 12,13-dibutyrate (PDBu) (10(-6) M) caused significant contractions that were completely inhibited by the PKC inhibitors staurosporine and calphostin C, no significant change in [Ca2+]i, and significant activation and translocation of the Ca(2+)-independent epsilon-PKC but not the Ca(2+)-dependent alpha-PKC. In Ca(2+)-free Krebs, a single application of PDBu produced maximal contraction and PKC activity after 30 min, which declined to basal levels in 3 h and remained steady for 24 h, but did not prevent subsequent increases in contraction and PKC activity with a new addition of PDBu and did not significantly decrease the amount of alpha- or epsilon-PKC. Repeated (five to eight) applications of PDBu in Ca(2+)-free Krebs at 3-h intervals completely inhibited subsequent increases in contraction and PKC activity to PDBu, ET-1, or PGF2alpha, and significantly decreased the amount of epsilon-PKC but not that of alpha-PKC. These results provide evidence that a Ca(2+)-independent coronary vasoconstriction induced by ET-1 and PGF2alpha is associated with activation of the epsilon-PKC isoform. The results suggest that, in coronary artery smooth muscle, downregulation of PKC is isoform specific and is more dependent on the frequency rather than the duration of PKC activation. The results also suggest that repeated downregulation of epsilon-PKC might play a role in preconditioning of the coronary artery against vasoconstriction by ET-1 and PGF2alpha.

Potassium channels modulate canine pulmonary vasoreactivity to protein kinase C activation

The role of Ca2+-activated K+-channel, ATP-sensitive K+-channel, and delayed rectifier K+-channel modulation in the canine pulmonary vascular response to protein kinase C (PKC) activation was determined in the isolated blood-perfused dog lung. Pulmonary vascular resistances and compliances were measured with vascular occlusion techniques. The PKC activators phorbol 12-myristate 13-acetate (PMA; 10(-7) M) and thymeleatoxin (THX; 10(-7) M) significantly increased pulmonary arterial and pulmonary venous resistances and pulmonary capillary pressure and decreased total vascular compliance by decreasing both microvascular and large-vessel compliances. The Ca2+-activated K+-channel blocker tetraethylammonium ions (1 mM), the ATP-sensitive K+-channel inhibitor glibenclamide (10(-5) M), and the delayed rectifier K+-channel blocker 4-aminopyridine (10(-4) M) potentiated the pressor response to both PMA and THX on the arterial and venous segments and also further decreased pulmonary vascular compliance. In contrast, the ATP-sensitive K+-channel opener cromakalim (10(-5) M) attenuated the vasoconstrictor effect of PMA and THX on both the arterial and venous vessels. In addition, membrane depolarization by 30 mM KCl elicited an increase in the pressor response to PMA. These results indicate that pharmacological activation of PKC elicits pulmonary vasoconstriction. Closure of the Ca2+-activated K+ channels, ATP-sensitive K+ channels, and delayed rectifier K+ channels as well as direct membrane depolarization by KCl potentiated the response to PMA and THX, indicating that K+ channels modulate the canine pulmonary vasoconstrictor response to PKC activation.

Protein kinase C promotes spontaneous relaxation of streptolysin-O-permeabilized smooth muscle cells from the guinea-pig stomach

Isolated single smooth muscle cells from the fundus of a guinea-pig stomach were permeabilized by use of streptolysin-O (0.5 U/ml). Most of the permeabilized cells responded to 0.6 microM Ca2+, but not to 0.2 microM Ca2+, with a resulting maximal cell shortening to approximately 71% of the resting cell length. These cells were relaxed again by washing with the Ca2+-free solution (2.5 nM free Ca2+) for 3-5 min. Addition of 10 microM acetylcholine (ACh) resulted in both a marked decrease in the concentration of Ca2+ required to trigger a threshold response and an increase in the maximal cell shortening, indicating that the cells retained the muscarinic receptor function. When the cell treated with a protein kinase C (PKC) inhibitor, K-252b (1 microM), for 3 min was exposed to 10 microM ACh in the presence of K-252b, the cell shortened within 2 min with a maximal cell shortening. When the cell shortening was induced by 10 microM ACh plus 1 microM Ca2+ in the presence of K-252b (1 microM) or more selective PKC inhibitors, such as calphostin C (1 microM) or PKC pseudosubstrate peptide (100 microM), the extension of the shortened cells, by washing with the Ca2+-free solution, was significantly inhibited. In contrast, K-252b (1 microM) did not inhibit the relaxation of Ca2+-induced shortened cells. These results suggest that the receptor-mediated activation of PKC in the process of ACh-induced cell shortening plays a role in the subsequent relaxation of the shortened cells.