Enhanced removal of Congo red dye from aqueous solution by surface modified activated carbon with bacteria

AIMS

The adsorption behaviour and mechanisms of the surface modified activated carbon with bacteria was evaluated.

METHODS AND RESULTS

16S rRNA was employed to identify the hydrocarbon-degrading bacteria. The bacteria was characterized by TEM and electron microscope. The surface modified activated carbon with bacteria was characterized by SEM. The adsorption behaviour was tested by static adsorption and dynamic adsorption.

CONCLUSION

The adsorption efficiency of the modified activated carbon was high when pH was weak acidic, and the adsorption capacity increased with the increase of temperature ranging from 20 to 35°C. The adsorption capacity peaked at 234·6 mg g^-1 at 25°C, which was sixfold higher than that of activated carbon. The pseudo-first-order kinetic can more accurately assess Congo red adsorption on the two adsorbents. The adsorption of Congo red by bacteria surface modified activated carbon fitted well with the Langmuir's model. The adsorption process was endothermic, and the biological floccules were formed during the adsorption. The physical adsorption is the main driving force.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that the bacteria surface-modified activated carbon can be used effectively as an adsorbent to eliminate Congo red from aqueous solutions.

[Complexity of Detecting CRISPR/Cas9-Mediated Homologous Recombination in Zebrafish]

Homology-directed (HD) genome modification offers an opportunity to precisely modify the genome. Despite reported successful cases, for many loci, precise genome editing remains challenging and inefficient in vivo. Here we report an effort to precisely knock-in a GFP reporter into gad locus mediated by CRISPR/Cas9 system in the zebrafish Danio rerio. PCR artifact was detected in testing for homologous recombination (HR), but was mitigated by optimizing PCR condition and decreasing the injected targeting plasmid concentration. Under this optimized condition, time course analysis revealed a decline of the HR-positive embryos at embryogenesis progressed. GFP signals also diminished at later developmental stages. The GFP signals were consistent with PCR detection, both of which suggested the loss of targeted insertion events at later stages. Such loss of insertion might be one underlying reason for the inability to obtain germ-line transgenic lines with GFP knocked into the gad locus. Our results suggest that the low HR efficiency associated with CRISPR-mediated knock-in is in part due to loss of insertion after targeted integration into the gad locus.

Sex-related differences in response to zinc pyrithione shampoo vs. non-anti-dandruff shampoo

OBJECTIVE

Sex-related differences in skin properties may be expected to impact dandruff formation and treatment. A meta-analysis approach was undertaken to investigate potential differences between males and females in response to zinc pyrithione (ZnPT) treatment vs. non-anti-dandruff (AD) shampoo. A separate pooled statistical analysis of ceramide and total protein loss endpoints was also undertaken to assess potential sex-related differences in stratum corneum properties that might influence response to ZnPT vs. non-AD shampoo in subjects with dandruff.

METHODS

The meta-analysis approach included data from 17 half-head, double-blind, randomized studies (N = 2088) undertaken in Asia to assess the effectiveness of 1% ZnPT shampoo and/or non-AD shampoo in reducing dandruff severity, as assessed by Total Weighted Head Score Adherent Flake (TWHS-AF) methodology. Treatment duration was 4 weeks, with TWHS-AF measured at weekly intervals. Data from an additional three studies (N = 143) conducted in Asia were included in the pooled analysis of ceramide levels and protein loss from scalp skin of subjects with dandruff.

RESULTS

Response to 1% ZnPT vs. non-AD shampoo was greater in males than in females at all time points; after 4 weeks, the between-treatment difference in TWHS-AF was -17.5 (95% confidence interval [CI] -19.5, -15.5) in males and -11.1 (-13.2, -8.9) in females. Sex-related differences were observed between males and females in response to both 1% ZnPT and non-AD shampoos. Males had a stronger response than females to treatment with 1% ZnPT shampoo, while dandruff decreased to a greater extent in females than in males when using non-AD shampoo. Statistically significant sex-related differences in ceramide levels and total protein loss were observed (both P < 0.01). Ceramide levels were 0.76 times lower (95% CI 0.60, 0.97) in males than in females, while total protein loss was 1.4 times greater (95% CI 1.1, 1.9) in males than in females.

CONCLUSION

Males show a greater response than females to 1% ZnPT shampoo, while females show a greater response than males to non-AD shampoo. These findings may in part be explained by the sex-related differences observed in stratum corneum properties, which may make males more prone to dandruff than females.

Effectiveness of rubber seed oil and flaxseed oil to enhance the α-linolenic acid content in milk from dairy cows

This experiment was conducted to investigate effect of rubber seed oil compared with flaxseed oil when fed alone or in combination on milk yield, milk composition, and α-linolenic acid (ALA) concentration in milk of dairy cows. Forty-eight mid-lactation Holstein dairy cows were randomly assigned to 1 of 4 treatments according to a completely randomized design. Cows were fed a basal diet (control; CON) or a basal diet supplemented with 4% rubber seed oil (RO), 4% flaxseed oil (FO), or 2% rubber seed oil plus 2% flaxseed oil (RFO) on a dry matter basis for 9 wk. Feed intake, milk protein percentage, and milk fat levels did not differ between the treatments. Cows fed the RO, FO, or RFO treatments had a higher milk yield than the CON group (up to 10.5% more), whereas milk fat percentages decreased. Compared with the CON, milk concentration of ALA was substantially higher in cows receiving RO or RFO, and was doubled in cows receiving FO. The ALA yield (g/d) increased by 31.0, 70.3, and 33.4% in milk from cows fed RO, FO, or RFO, respectively, compared with the CON. Both C18:1 trans-11 (vaccenic acid) and C18:2 cis-9,trans-11 (conjugated linoleic acid; CLA) levels were higher in cows fed added flaxseed or rubber seed oil. The CLA yield (g/d) increased by 336, 492, and 484% in cows fed RO, FO, or RFO, respectively, compared with the CON. The increase in vaccenic acid, ALA, and CLA was greater in cows fed RFO than in cows fed RO alone. Compared with the CON, the milk fat from cows fed any of the dietary supplements had a higher concentration of unsaturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids; conversely, the saturated fatty acids levels in milk fat were 30.5% lower. Insulin and growth hormones were not affected by dietary treatments; however, we noted an increase in both cholesterol and nonesterified fatty acids levels in the RO, FO, or RFO treatments. These results indicate that rubber seed oil and flaxseed oil will increase milk production and the concentration of functional fatty acids (ALA, vaccenic acid, and CLA) in milk fat while decreasing the content of saturated fatty acids.

Intra-articular delivery of anti-Hif-2α siRNA by chondrocyte-homing nanoparticles to prevent cartilage degeneration in arthritic mice

Hypoxia-inducible factor-2α (Hif-2α) is a potential therapeutic target for osteoarthritis (OA), but the application of this target in the delivery of therapeutic agents to chondrocytes remains a challenge. A chondrocyte-targeting vector was constructed in a previous study to enhance transfection efficiency and specificity of chondrocytes in vivo. This study used vectors to deliver small-interfering RNA (siRNA) and silenced Hif-2α expression to prevent cartilage degeneration in OA-affected mice. After siRNA transfection was conducted by cartilage-targeting nanoparticles, the protein levels of Hif-2α, matrix metalloproteinases (MMP-13, -9), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-4, -5), vascular endothelial growth factor (VEGF), type X collagen and nuclear factor (NF)-κB in interleukin-1-beta (IL-1β)-stimulated chondrocytes were determined. Chondrocyte-targeting ability was also determined by fluorescein isothiocyanate (FITC)-labeled siRNA tracking under a confocal microscope. OA model was established by surgically destabilizing the knee joints of a mouse. Hif-2α siRNA was then delivered intra-articularly with nanoparticles in vivo. Cartilage degeneration and synovium inflammation in the knee joints were analyzed by histomorphometry. IL-1β levels in the synovial fluid were also measured by enzyme-linked immunosorbent assay. In vitro assay results showed that catabolic factors, including Hif-2α, MMP-13 and -9, ADAMTS-4, VEGF, collagen type X and NF-κB, were downregulated after Hif-2α-siRNA transfection by chondrocyte-targeting nanoparticles. In vivo assay results with FITC-labeled siRNA tracking also confirmed that nanoparticles promoted the local concentration and prolonged the retention time of siRNA in the cartilage. Histological analysis results confirmed that nanoparticle-mediated siRNA maintained cartilage integrity and alleviated synovium inflammation. IL-1β levels decreased after siRNA was silenced by nanoparticles. Thus, chondrocyte-targeting nanoparticles could deliver Hif-2α siRNA to cartilage and specifically inhibit the expression of catabolic proteins.

TRPV1 activation impedes foam cell formation by inducing autophagy in oxLDL-treated vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) are an important origin of foam cells besides macrophages. The mechanisms underlying VSMC foam cell formation are relatively little known. Activation of transient receptor potential vanilloid subfamily 1 (TRPV1) and autophagy have a potential role in regulating foam cell formation. Our study demonstrated that autophagy protected against foam cell formation in oxidized low-density lipoprotein (oxLDL)-treated VSMCs; activation of TRPV1 by capsaicin rescued the autophagy impaired by oxLDL and activated autophagy–lysosome pathway in VSMCs; activation of TRPV1 by capsaicin impeded foam cell formation of VSMCs through autophagy induction; activation of TRPV1 by capsaicin induced autophagy through AMP-activated protein kinase (AMPK) signaling pathway. This study provides evidence that autophagy plays an important role in VSMC foam cell formation and highlights TRPV1 as a promising therapeutic target in atherosclerosis.

Microstructural characterization of Ti-6Al-4V alloy subjected to the duplex SMAT/plasma nitriding

In this study, microstructural characterization of Ti-6Al-4V alloy, subjected to the duplex surface mechanical attrition treatment (SMAT)/nitriding treatment, leading to improve its mechanical properties, was carried out through novel and original samples preparation methods. Instead of acid etching which is limited for morphological characterization by scanning electron microscopy (SEM), an original ion polishing method was developed. Moreover, for structural characterization by transmission electron microscopy (TEM), an ion milling method based with the use of two ions guns was also carried out for cross-section preparation. To demonstrate the efficiency of the two developed methods, morphological investigations were done by traditional SEM and field emission gun SEM. This was followed by structural investigations through selected area electron diffraction (SAED) coupled with TEM and X-ray diffraction techniques. The results demonstrated that ionic polishing allowed to reveal a variation of the microstructure according to the surface treatment that could not be observed by acid etching preparation. TEM associated to SAED and X-ray diffraction provided information regarding the nanostructure compositional changes induced by the duplex SMAT/nitriding process.

Surface nanocrystallization of Ti-6Al-4V alloy: microstructural and mechanical characterization

In this study, microstructural and mechanical properties of Ti-6Al-4V alloy, before and after the SMA treatment (SMAT) as well as the duplex SMAT/Nitriding process at different treatment conditions, were investigated in order to deepen the knowledge of these properties for biomedical devices. For that purpose, tribological (wear resistance, coefficient of friction) and mechanical (Vickers microhardness) tests were performed. To carry out the microstructural and surface topographical characterization of the samples, the scanning electron microscopy (SEM) and the 3D-SEM reconstruction from stereoscopic images have been used. By means of profiles deduced from the 3D images, the surface roughness has been calculated. The obtained results allowed to find an interesting SMAT condition which, followed by nitriding at low temperature, can greatly improve tribological and mechanical properties of Ti-6Al-4V alloy. It was also shown from SEM characterization and the original method of 3D-SEM reconstruction, that SMAT can reduce the machined grooves and consequently the roughness of the samples decreases. Moreover, we demonstrated, for the first time, that instead of usual etching method, the ionic polishing allowed to reveal the grains, the grain boundaries and the twins as well as the surface nanocrystalline layer generated by SMAT. Thus, the thickness of the SMATed layer decreases with the nitriding temperature, whereas the surface grain size increases.

Molecular cloning and mRNA expression profiling of the first specific jasmonate biosynthetic pathway gene allene oxide synthase from Hyoscyamus niger

In the endeavor to enhance the production of pharmaceutically valuable tropane alkaloids including hyoscyamine and scopolamine in Hyoscyamus niger, methyl jasmonate (MeJA) showed significant stimulation both in tropane biosynthetic pathway enzymes activities and tropane alkaloids yields. Therefore it was speculated that genetic engineering of jasmonate biosynthetic pathway might enhance the endogenous jasmonate concentration, followed by stimulating the production of tropane alkaloids. Herein a full-length cDNA encoding allene oxide synthase (AOS, EC 4.2.1.92), the first committed step enzyme in jasmonate biosynthetic pathway was reported (named HnAOS, GenBank accession: EF532599). HnAOS was a novel member of the cytochrome P450 (CYP74A) subfamily. Real-time quantitative PCR analysis showed that HnAOS mRNA accumulated mainly in stems, and responded significantly to wounding or methyl jasmonate.

[Molecular cloning and expression profile of a jasmonate biosynthetic pathway gene allene oxide cyclase from Hyoscyamus niger]

Hyoscyamus niger L. is a medicinal plant which produces a class of jasmonate-responsive pharmaceutical secondary metabolites named as tropane alkaloids. As a family of signaling phytohormones, jasmonates play significant roles in the biosynthesis of many plant secondary metabolites. In jasmonate biosynthetic pathway of plants, allene oxide cyclase (AOC, [...] EC 5.3.99.6 [...]) catalyzes the most important step. Here we cloned a cDNA from H. niger, named HnAOC (GenBank accession: AY708383), which was 1044 bp long, with a 747 bp open reading frame (ORF) encoding a polypeptide of 248 amino acid residues. Southern blot analysis indicated that it was a multi-copy gene. RT-PCR analysis revealed that the expression of HnAOC was regulated by various stresses and elicitors, with methyl-jasmonate showing the most prominent inducement. The characterization of HnAOC would be helpful for improving the production of valuable secondary metabolites by regulating the biosynthesis ofjasmonates.

Paradoxical Cellular Ca 2+ Signaling in Severe but Compensated Canine Left Ventricular Hypertrophy

In conscious dogs with severe left ventricular (LV) hypertrophy (H) (doubling of LV/body weight), which developed gradually over 1 to 2 years after aortic banding, baseline LV function was well compensated. The LV was able to generate twice the LV systolic pressure without an increase in LV end-diastolic pressure, or decrease in LV dP/dt or LV wall thickening. However, LV myocytes isolated from LVH dogs exhibited impaired contraction at baseline and in response to Ca 2+ . There was no change in L-type Ca 2+ channel current ( I Ca ) density but the ability of I Ca to trigger Ca 2+ release from the sarcoplasmic reticulum (SR) was reduced. Immunoblot analysis revealed a 68% decrease in SERCA2a, and a 35% decrease in the number of ryanodine receptors (RyR2), with no changes in protein level of calsequestrin, Na + /Ca 2+ exchanger or phospholamban (PLB), but with both RyR2 and PLB hyperphosphorylated. Spontaneous Ca 2+ sparks in LVH cells were found to have prolonged duration but similar intensities despite the reduced SR Ca 2+ load. A higher Ca 2+ spark rate was observed in LVH cells, but this is inconsistent with the reduced SR Ca 2+ content. However, Ca 2+ waves were found to be less frequent, slower and were more likely to be aborted in Ca 2+ -challenged LVH cells. These paradoxical observations could be accounted for by a nonuniform SR Ca 2+ distribution, RyR2 hyperphosphorylation in the presence of decreased global SR Ca 2+ load. We conclude that severe LVH with compensation masks cellular and subcellular Ca 2+ defects that remain likely contributors to the limited contractile reserve of LVH.

[Isolation and expression profiling of the Pto-like gene SsPto from Solanum surattense]

A novel Pto-like gene (designated as SsPto) is cloned from yellow-fruit nightshade (Solanum surattense). The full-length cDNA of SsPto is 1331 bp long with an open reading frame of 960 bp encoding a polypeptide of 320 amino acid residues. The deduced SsPto protein has a calculated molecular weight of 36.21 kDa with an isoelectric point of 6.18. Multiple sequence alignment shows that SsPto protein shares 71.4% and 71.6% identities to Pto proteins from Lycopersicon pimpinellifolium and L. hirsutum respectively. Genomic Southern blot analysis indicates the presence of a small family of SsPto in the S. surattense genome. SsPto is found to be constitutively expressed in the S. surattense plant with the highest expression in stems. However, under induction by TMV for 6 days, SsPto expresses the highest in roots. Further expression analysis reveals that the signaling components of defense/stress pathways, such as methyl jasmonate (MeJA), salicylic acid (SA), gibberellic acid (GA3) and hydrogen peroxide (H2O2), up-regulate the SsPto transcript levels over the control. Cold treatment, nevertheless, has no significant effect on SsPto expression whereas SsPto expression is down-regulated by dark treatment. Our findings suggest that this novel stress- and pathogen-inducible SsPto from S. surattense may participate not only in the defense/stress responsive pathways, but also in diverse processes of plant's growth and development.

Diacylglycerol and fatty acids synergistically increase cardiomyocyte contraction via activation of PKC

Lipid signaling pathways are thought to play a prominent role in transducing extracellular signals into contractile responses in cardiac muscle. Two putative lipid messengers, diacyglycerol and arachidonic acid, can be generated via distinct phospholipases in separate signaling pathways, but certain stimuli cause them to be elevated in parallel. We tested the hypothesis that these lipids function as comessengers in ventricular myocytes by activating protein kinase C (PKC). In previous work, we demonstrated that the diacylglycerol analog dioctanoylglycerol (diC(8)) can be stimulatory or inhibitory toward myocyte twitches depending on how it is applied. Here we report that arachidonic acid and other cis-unsaturated fatty acids (UFA), at concentrations too low for direct effects, synergistically enhance the stimulatory effects of diC(8) and convert inhibitory effects of diC(8) into stimulation of myocyte twitches. Intracellular Ca(2+) transients changed in parallel with twitch amplitude, suggesting regulation of Ca(2+) homeostasis by these lipids. cis-UFA also interacted synergistically with the PKC activator phorbol 12-myristate 13-acetate to promote positive inotropic responses. Responses were blocked by the PKC antagonists chelerythrine chloride, bisindolylmaleimide, and Gö-6976. DiC(8) and arachidonic acid also synergistically translocated PKC-epsilon and PKC-alpha in intact myocytes. We propose that PKC integrates diacylglycerol and cis-UFA signals in the heart, resulting in preferential activation of positive inotropic mechanisms.

Endothelin-1 and photoreleased diacylglycerol increase L-type Ca2+ current by activation of protein kinase C in rat ventricular myocytes

The amphotericin B-perforated whole-cell patch clamp technique was used to determine the modulation of L-type Ca2+ channels by protein kinase C (PKC)-mediated pathways in adult rat ventricular myocytes. Application of 10 nM endothelin-1 (ET-1) increased peak Ca2+ current (ICa) by 28.2 +/- 2.5 % (n = 13) and slowed current decay. These effects were prevented by the endothelin receptor antagonist PD145065 (10 microM) and by the PKC inhibitor chelerythrine (8 microM). To establish if direct activation of PKC mimicked the ET-1 effect, the active and inactive phorbol esters (phorbol-12-myristate-13-acetate and 4alpha-phorbol-12, 13-didecanoate) were tested. Both phorbol esters (100 nM) resulted in a small (approximately 10%) increase in ICa, suggesting PKC-independent effects. Bath application of dioctanoylglycerol (diC8), a diacylglycerol (DAG) analogue which is capable of directly activating PKC, caused a gradual decline in peak ICa (50.4 +/- 6.2 %, n = 5) and increased the rate of current decay. These effects were unaffected by the PKC inhibitor chelerythrine (8 microM). Intracellular photorelease of caged diC8 with 3 or 10 s exposure to UV light produced a concentration-dependent increase in peak ICa (20. 7 +/- 8.5 % (n = 8) for 3 s UV and 60.8 +/- 11.4 % (n = 13) for 10 s UV), which could be inhibited by chelerythrine. Our results demonstrate that both ET-1 and intracellularly photoreleased diC8 increase ICa by a PKC-mediated pathway, which is in direct contrast to the PKC-independent inhibition of ICa produced by bath-applied diC8. We conclude that specific cellular pools of DAG are crucially important in the regulation of ICa by PKC.

Cardiac troponin I gene knockout: a mouse model of myocardial troponin I deficiency

Troponin I is a subunit of the thin filament-associated troponin-tropomyosin complex involved in calcium regulation of skeletal and cardiac muscle contraction. We deleted the cardiac isoform of troponin I by using gene targeting in murine embryonic stem cells to determine the developmental and physiological effects of the absence of this regulatory protein. Mice lacking cardiac troponin I were born healthy, with normal heart and body weight, because a fetal troponin I isoform (identical to slow skeletal troponin I) compensated for the absence of cardiac troponin I. Compensation was only temporary, however, as 15 days after birth slow skeletal troponin I expression began a steady decline, giving rise to a troponin I deficiency. Mice died of acute heart failure on day 18, demonstrating that some form of troponin I is required for normal cardiac function and survival. Ventricular myocytes isolated from these troponin I-depleted hearts displayed shortened sarcomeres and elevated resting tension measured under relaxing conditions and had a reduced myofilament Ca sensitivity under activating conditions. The results show that (1) developmental downregulation of slow skeletal troponin I occurs even in the absence of cardiac troponin I and (2) the resultant troponin I depletion alters specific mechanical properties of myocardium and can lead to a lethal form of acute heart failure.

Role of intracellular Ca2+ and pH in positive inotropic response of cardiomyocytes to diacylglycerol

Diacylglycerol has been hypothesized to mediate the positive inotropic response of myocardium to the alpha-adrenergic agonists angiotensin II and endothelin. The mechanism of action of diacylglycerol was examined here in adult rat ventricular myocytes by releasing dioctanoylglycerol (diC8) intracellularly from a caged compound while monitoring Ca2+ transients and pH with fluorescent indicators. DiC8 caused a three- to fourfold increase in twitch amplitude and a twofold increase in the systolic Ca2+ transient. No other parameter was consistently influenced by diC8, including the kinetics of Ca2+ cycling, the Ca2+ content of the sarcoplasmic reticulum, or the myofilament Ca2+ sensitivity. DiC8 also had no detectable effect on intracellular pH or Na+/H+ antiport activity. Consistent with this finding, the Na+/H+ exchange inhibitor N-ethylisopropyl amiloride was without effect on the positive inotropic response to diC8. The marked enhancement of systolic Ca2+ by diC8 suggests that the process of excitation-contraction coupling is an important and possibly preferred target of diacylglycerol-protein kinase C signaling in myocardium.

Arachidonic acid stimulates protein kinase C-epsilon redistribution in heart cells

Arachidonic acid is elevated in a variety of cell types in response to extracellular stimuli, and has been hypothesized to exert at least some of its intracellular actions via activation of protein kinase C. Here we show that arachidonic acid stimulates a unique pattern of translocation of the epsilon-isoform of protein kinase C in isolated adult rat cardiac myocytes. Using western blot analysis, the majority of epsilon-protein kinase C was found in a cytosolic fraction in unstimulated cells. Treatment with 50 microM arachidonic acid caused a transient increase of epsilon-protein kinase C in a membrane fraction within 1 minute, then after 5–20 minutes most was found in a filament/nuclear fraction. Immunofluorescence and confocal microscopy of the filament fraction revealed a striated staining pattern with epsilon-protein kinase C localized near the Z-line where actin filaments are anchored and where transverse tubules are closely apposed to the myofilaments. delta-Protein kinase C, another isoform highly expressed in these cells, did not redistribute significantly in response to arachidonic acid, but in response to phorbol ester displayed a predominantly nuclear localization. Arachidonic acid also stimulated phosphorylation of the thin filament protein, troponin I, consistent with a filament localization for activated PKC. The physiological relevance of these findings was supported by the observation that 50 microM arachidonic acid promoted a 2.3-fold enhancement of myocyte twitch amplitude, an effect that was significantly blocked by the protein kinase C antagonist chelerythrine. Moreover, the onset of this physiological response correlated in time with translocation of epsilon-protein kinase C to the filaments. The results suggest that arachidonic acid initiates a redistribution of epsilon-protein kinase C to myofilament structures at or near the Z-line where this isozyme would be strategically located to regulate myofilament function and excitation-contraction coupling.

Positive inotropy mediated by diacylglycerol in rat ventricular myocytes

Many neurohormones stimulate phospholipid hydrolysis and elevate diacylglycerol in the mammalian heart, but the physiological consequences of these intracellular events are unclear. Regulation of myocardial contraction by diacylglycerol was investigated in the present study by releasing the diacylglycerol analogue dioctanoylglycerol (diC8) within adult rat ventricular myocytes by using a light-sensitive caged compound. This approach permitted us to avoid exposure of myocytes to extracellular diC8 and yet to control the amount of diC8 released into the cells. Photorelease of diC8 produced a slowly developing (half-time, 1.9 +/- 0.1 minute; n = 26) but robust (406 +/- 42%) enhancement of twitch amplitude in electrically paced myocytes (0.5 Hz, 1 mmol/L Ca2+, Ringer's solution [pH 7.4], 22 degrees C). This positive inotropic effect was dose dependent, stereospecific for the S-enantiomer of diC8, synergistically enhanced by arachidonic acid, and blocked by the protein kinase C inhibitor chelerythrine. The data provide evidence that diacylglycerol can induce a strong positive inotropic effect in mammalian ventricular muscle, possibly by activating protein kinase C. By contrast, perfusion of diC8 extracellularly onto myocytes caused a 42 +/- 2% decline in twitch amplitude, in accordance with previous reports. To account for this dependence on how diC8 is applied, we postulate that diC8 has distinct physiological actions at intracellular and extracellular sites. The peptide neurohormone endothelin-1, which elevates diacylglycerol in cardiac tissues, produced a positive inotropic effect that was similar to the response to photoreleased diC8. The diacylglycerol/protein kinase C pathway has now become a good candidate for mediator of at least a component of the positive inotropy associated with agents that stimulate phospholipid turnover in adult mammalian myocardium.