Cx43-Delivered miR-181b Negatively Regulates Sirt1/FOXO3a Signalling Pathway-Mediated Apoptosis on Intestinal Injury in Sepsis

INTRODUCTION

Gap junctions can transmit signals between cells, including miRNAs, leading to the amplification of adjacent cell damage. No previous study has addressed gap junctions and miRNAs in sepsis because the internal mechanism of sepsis-induced intestinal injury is complex. Therefore, we studied the relationship between connexin43 (Cx43) and miR-181b and provided a research direction for further study of sepsis.

METHODS

A mouse caecal ligation and puncture method was used to construct a mouse sepsis model. Firstly, damage to intestinal tissues at different time points was analysed. The levels of Cx43, miR-181b, Sirt1, and FOXO3a in intestinal tissues and the transcription and translation of the apoptosis-related genes Bim and puma, which are downstream of FOXO3a were analysed. Secondly, the effect of Cx43 levels on miR-181b and Sirt1/FOXO3a signalling pathway activity was explored by using the Cx43 inhibitor heptanol. Finally, luciferase assays were used to determine miR-181b binding to the predicted target sequence.

RESULTS

The results show that during sepsis, intestinal injury becomes increasingly worse with time, and the expression of Cx43 and miR-181b increase. In addition, we found that heptanol could significantly reduce intestinal injury. This finding indicates that inhibiting Cx43 regulates the transfer of miR-181b between adjacent cells, thereby reducing the activity of the Sirt1/FOXO3a signalling pathway and reducing the degree of intestinal injury during sepsis.

CONCLUSIONS

In sepsis, the enhancement of Cx43 gap junctions leads to an increase in miR-181b intercellular transfer, affects the downstream SIRT1/FOXO3a signalling pathway and causes cell and tissue damage.

Virus-induced plant volatiles mediate the olfactory behaviour of its insect vectors

Plant viruses can manipulate their hosts to release odours that are attractive or repellent to their insect vectors. However, the volatile organic compounds (VOCs), either individually or as mixtures, which play a key role in the olfactory behaviour of insect vectors remains largely unknown. Our study focused on green rice leafhoppers (GRLHs) vectoring rice dwarf virus (RDV) revealed that RDV infection significantly induced the emission of (E)-β-caryophyllene and 2-heptanol by rice plants, which influenced the olfactory behaviour of both non-viruliferous and viruliferous GRLHs. (E)-β-caryophyllene attracted non-viruliferous GRLHs to settle on RDV-infected plants, but neither attracted nor repelled viruliferous GRLHs. In contrast, 2-heptanol repelled viruliferous GRLHs to settle on RDV-infected plants, but neither repelled nor attracted non-viruliferous GRLHs. Suppression of (E)-β-caryophyllene synthase OsCAS via CRISPR-Cas9 to generate oscas-1 plants enabled us to confirm the important role played by (E)-β-caryophyllene in modulating the virus-vector-host plant interaction. These novel results reveal the role of these virus-induced VOCs in modulating the behaviour of its GRLH insect vector and may facilitate the design of new strategies for disease control through manipulation of plant volatile emissions.

Serum lipidomics analysis of ovariectomized rats under Curcuma comosa treatment

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma comosa Roxb. (C. comosa) or Wan Chak Motluk, Zingiberaceae family, has been used in Thai traditional medicine for the treatment of gynecological problems and inflammation.

AIM OF THE STUDY

This study aimed to investigate the therapeutic potential of C. comosa by determining the changes in the lipid profiles in the ovariectomized rats, as a model of estrogen-deficiency-induced hyperlipidemia, after treatment with different components of C. comosa using an untargeted lipidomics approach.

MATERIALS AND METHODS

Lipids were extracted from the serum of adult female rats subjected to a sham operation (SHAM; control), ovariectomy (OVX), or OVX with 12-week daily doses of estrogen (17β-estradiol; E₂), (3R)-1,7-diphenyl-(4E,6E)-4,6-heptadien-3-ol (DPHD; a phytoestrogen from C. comosa), powdered C. comosa rhizomes or its crude ethanol extract. They were then analyzed by liquid chromatography-mass spectrometry, characterized, and subjected to the orthogonal projections to latent structures discriminant analysis statistical model to identify tentative biomarkers.

RESULTS

Levels of five classes of lipids (ceramide, ceramide-1-phosphate, sphingomyelin, 1-O-alkenyl-lysophosphatidylethanolamine and lysophosphatidylethanolamine) were elevated in the OVX rats compared to those in the SHAM rats, while the monoacylglycerols and triacylglycerols were decreased. The E₂ treatment only reversed the levels of ceramides, whereas treatments with DPHD, C. comosa extract or powder returned the levels of all upregulated lipids back to those in the SHAM control rats.

CONCLUSIONS

The findings suggest the potential beneficial effects of C. comosa on preventing the increased ceramide levels in OVX rats, a possible cause of metabolic disturbance under estrogen deficiency. Overall, the results demonstrated the power of untargeted lipidomics in discovering disease-relevant biomarkers, as well as evaluating the effectiveness of treatment by C. comosa components (DPHD, extract or powder) as utilized in Thai traditional medicine, and also providing scientific support for its folklore use.

Atrial Anti-Arrhythmic Effects of Heptanol in Langendorff-Perfused Mouse Hearts

Acute effects of heptanol (0.1 to 2 mM) on atrial electrophysiology were explored in Langendorff-perfused mouse hearts. Left atrial bipolar electrogram or monophasic action potential recordings were obtained during right atrial stimulation. Regular pacing at 8 Hz elicited atrial activity in 11 out of 11 hearts without inducing atrial arrhythmias. Programmed electrical stimulation using a S1S2 protocol provoked atrial tachy-arrhythmias in 9 of 17 hearts. In the initially arrhythmic group, 2 mM heptanol exerted anti-arrhythmic effects (Fisher’s exact test, P < 0.05) and increased atrial effective refractory period (ERP) from 26.0 ± 1.9 to 57.1 ± 2.5 ms (ANOVA, P < 0.001) despite increasing activation latency from 18.7 ± 1.1 to 28.9 ± 2.1 ms (P < 0.001) and leaving action potential duration at 90% repolarization (APD₉₀) unaltered (25.6 ± 1.2 vs. 27.2 ± 1.2 ms; P > 0.05), which led to increases in ERP/latency ratio from 1.4 ± 0.1 to 2.1 ± 0.2 and ERP/APD₉₀ ratio from 1.0 ± 0.1 to 2.1 ± 0.2 (P < 0.001). In contrast, in the initially non-arrhythmic group, heptanol did not alter arrhythmogenicity, increased AERP from 47.3 ± 5.3 to 54.5 ± 3.1 ms (P < 0.05) and activation latency from 23.7 ± 2.2 to 31.3 ± 2.5 ms and did not alter APD₉₀ (24.1 ± 1.2 vs. 25.0 ± 2.3 ms; P > 0.05), leaving both AERP/latency ratio (2.1 ± 0.3 vs. 1.9 ± 0.2; P > 0.05) and ERP/APD₉₀ ratio (2.0 ± 0.2 vs. 2.1 ± 0.1; P > 0.05) unaltered. Lower heptanol concentrations (0.1, 0.5 and 1 mM) did not alter arrhythmogenicity or the above parameters. The present findings contrast with known ventricular pro-arrhythmic effects of heptanol associated with decreased ERP/latency ratio, despite increased ERP/APD ratio observed in both the atria and ventricles.

Protocols to Study Behavior in Drosophila

Drosophila melanogaster is an incredibly versatile organism capable of both innate and higher-order behaviors. These behaviors offer not only a way to assay whether or not the animal is physiologically compromised (e.g., feeding, locomotion), but also serve to assess changes in centrally mediated functions. Here we describe several high throughput, reproducible, yet inexpensive and facile behavioral assays for both larval and adult Drosophila. The larval assays all employ an agar substrate in a petri dish; the adult assays are grouped into "vial-based" and "arena-based" paradigms. While these protocols are largely designed to assess individual animals, they are sufficiently rapid that ample numbers can be tested to determine behavioral significance. Importantly, this also allows for one to control for reproductive status, age, and sex, since these factors all have a significant impact on adult behaviors. In general, it is best to designate a dedicated area for any assay, so that lighting conditions are consistent, and all animals should be tested at roughly the same time each day to minimize circadian fluctuations. Temperature and humidity should also be maintained at a constant level to minimize variability in the assays.

Dysfunction in gap junction intercellular communication induces aberrant behavior of the inner cell mass and frequent collapses of expanded blastocysts in mouse embryos

PURPOSE

We investigated the role of gap junctions (GJs) in embryological differentiation, and observed the morphological behavior of the inner cell mass (ICM) by time-lapse movie observation (TLM) with gap junction inhibitors (GJis).

METHODS

ICR mouse embryos were exposed to two types of GJis in CZB medium: oleamide (0 to 50 μM) and 1-heptanol (0 to 10 mM). We compared the rate of blastocyst formation at embryonic day 4.5 (E4.5) with E5.5. We also observed and evaluated the times from the second cleavage to each embryonic developing stage by TLM. We investigated embryonic distribution of DNA, Nanog protein, and Connexin 43 protein with immunofluorescent staining.

RESULTS

In the comparison of E4.5 with E5.5, inhibition of gap junction intercellular communication (GJIC) delayed embryonic blastocyst formation. The times from the second cleavage to blastocyst formation were significantly extended in the GJi-treated embryos (control vs with oleamide, 2224 ± 179 min vs 2354 ± 278 min, p = 0.013). Morphological differences were traced in control versus GJi-treated embryos until the hatching stage. Oleamide induced frequent severe collapses of expanded blastocysts (77.4 % versus 26.3 %, p = 0.0001) and aberrant ICM divisions connected to sticky strands (74.3 % versus 5.3 %, p = 0.0001). Immunofluorescent staining indicated Nanog-positive cells were distributed in each divided ICM.

CONCLUSIONS

GJIC plays an important role in blastocyst formation, collapses of expanded blastocysts, and the ICM construction in mouse embryos.

Heptanol triggers cardioprotection via mitochondrial mechanisms and mitochondrial potassium channel opening in rat hearts

AIM

To investigate mechanisms behind heptanol (Hp)-induced infarct size reduction and in particular if protection by pre-treatment with Hp is triggered through mitochondrial mechanisms.

METHODS

Langendorff perfused rat hearts, isolated mitochondria and isolated myocytes were used. Infarct size, mitochondrial respiration, time to mitochondrial permeability transition pore (MPTP) opening and AKT and glycogen synthase kinase 3 beta (GSK-3β) phosphorylation were examined.

RESULTS

Pre-treatment with Hp reduced infarct size from 29.7 ± 3.4% to 12.6 ± 2.1%. Mitochondrial potassium channel blockers 5-hydroxy decanoic acid (5HD) blocking mitoK(ATP) and paxilline (PAX) blocking mitoK(Ca) abolished cardioprotective effect of Hp (Hp + 5HD 36.7 ± 2.9% and Hp + PAX 40.2 ± 2.8%). Hp significantly reduced respiratory control ratio in both subsarcolemmal and interfibrillar mitochondria in a dose-dependent manner (0.5-5.0 mm). The ADP oxygen ratio was also significantly reduced by Hp (2 mm). Laser scanning confocal microscopy of tetramethylrhodamine-loaded isolated rat myocytes using line scan mode showed that Hp increased time to MPTP opening. Western blot analysis showed that pre-treatment with Hp increased phosphorylation of AKT and GSK-3β before ischaemia and after 30 min of global ischaemia.

CONCLUSION

Pre-treatment with Hp protects the heart against ischaemia-reperfusion injury. This protection is most likely mediated via mitochondrial mechanisms which initiate a signalling cascade that converges on inhibition of opening of MPTP.

Damaging effect of cumulus denudation on rabbit oocytes

OBJECTIVE

To study the effect of cumulus denudation on in vitro maturation of rabbit oocytes.

DESIGN

Experimental animal study.

SETTING

Academic institution.

ANIMAL(S)

Rabbits and mice.

INTERVENTION(S)

Rabbit oocytes were observed compared with mouse oocytes.

MAIN OUTCOME MEASURE(S)

Developmental competence, membrane integrity, and apoptotic status of oocytes after cumulus denudation.

RESULT(S)

Although in vitro maturation of mouse cumulus-denuded oocytes was unaffected, rabbit cumulus-denuded oocytes could not mature. However, 50% of rabbit cumulus-intact oocytes matured normally when their gap junctions were sealed with 1-heptanol. Coculture with cumulus cells did not improve maturation of rabbit cumulus-denuded oocytes unless with an intact corona radiata. Staining with Hoechst 33258, Bcl-2 antibodies, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling showed membrane breaches or apoptosis of rabbit cumulus-denuded oocytes, contrary to the mouse cumulus-denuded oocytes. Ultrastructurally, rabbit oocytes showed no perivitelline space but numerous long cell junctions projecting into the egg cortex, contrary to the mouse oocytes. However, the damaging effect of cumulus denudation was much relieved after preincubation of rabbit cumulus-intact oocytes with phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, and some cumulus-denuded oocytes prepared after preincubation matured and developed into blastocysts.

CONCLUSION(S)

[1] Cumulus denudation severely damaged rabbit oocytes leading to their apoptosis or degeneration, possibly because of the deep-set junctional complexes anchoring the oocyte and corona cells; and [2] preincubation with phosphodiesterase inhibitor may provide a method to avoid the damaging effect of cumulus denudation on rabbit oocytes.

Gap junction channel modulates pulmonary vascular permeability through calcium in acute lung injury: an experimental study

BACKGROUND

Increased pulmonary vascular permeability is a hallmark of acute lung injury (ALI). Gap junction channels (GJCs) connect adjacent cells and facilitate ion exchange. It remained unclear whether GJCs modulate pulmonary permeability in ALI through intracellular calcium.

OBJECTIVES

This study aimed to verify if GJCs in pulmonary microvessel endothelial cells (PMVECs) modulate pulmonary vascular permeability in ALI via intracellular calcium.

METHODS

Firstly, an animal model of ALI was studied using connexin 40 (Cx40) immunohistochemistry in the lung with Evans' blue (EB) leakage. Then cultured PMVECs were divided into three groups: G(control), G(serum) and G(blocker). Serum was obtained from animals with ALI following gunshot injury (injured serum). Initially, G(blocker) was treated with the blocker of GJCs, and then G(serum) and G(blocker) were stimulated with the injured serum, respectively. GJCs, the permeability of cell monolayers and intracellular Ca(2+) were assessed.

RESULTS

Cx40 time-dependently decreased, whereas EB leakage increased. Cx40 and EB leakage exhibited a strong inverse correlation (rho = -0.934, p < 0.05). Injured serum decreased GJCs and expression of Cx40, whereas the blocker aggravated this effect. Similarly, when PMVEC monolayer was treated with injured serum, both permeability and intracellular Ca(2+) increased. These effects were also aggravated with the blocker.

CONCLUSIONS

Depression of GJCs of PMVECs increased pulmonary vascular permeability in ALI; this effect may be mediated by the overload of intracellular calcium.

[Effect of gap junction on the cardioprotection of ischemic postconditioning in rat heart]

AIM

To determine whether the cardioprotection of ischemic postconditioning and heptanol in ischemic heart against ischemia/reperfusion (I/R) is mediated by gap junction.

METHODS

The effect of ischemic postconditioning, heptanol at different doses (0.03, 0.06, 0.30, and 0.60 mg/kg) and AAP10 (10 mg/kg) on the intact rat heart during 30 min ischemia and 2 h of reperfusion was observed. Ischemic postconditioning was achieved by 3 cycles of 10 s reperfusion/10 s regional ischemia starting at the beginning of the reperfusion. The infarct size and the arrhythmia scores were measured. The effect of ischemic postconditioning, heptanol at different doses (0.05, 0.10, 0.50 and 1.00 mmol/L) and AAP10 (1 x 10(-7)mol/L) on the isolated heart during 30 min ischemia and 2 h of reperfusion was observed. Ischemic postconditioning was achieved by 6 cycles of 10 s reperfusion/10 s global ischemia starting at the beginning of the reperfusion. The arrhythmia scores and conduction velocity of ventricle muscle were measured.

RESULTS

In the intact rat heart model, ischemic postconditioning and heptanol reduced infarct size and arrhythmia scores. In the Langendorff perfused rat heart model, ischemic postconditioning and heptanol reduced arrhythmia scores and conduction velocity of ventricle muscle. Administration of AAP10, an opener of gap junction attenuated the cardioprotection of ischemic postconditioning and heptanol.

CONCLUSION

The cardioprotection of ischemic postconditioning and heptanol may be related to the attenuation of gap junction communication on myocardiac ischemia/reperfusion injury.

Reducing the cyclic variations of ultrasonic integrated backscatters and myocardial electrical synchronism by reversibly blocking intercellular communications with heptanol

The purpose of this study is to provide direct evidence for the role of intercellular communications in electrical synchronization and mechanical function of myocardium. We used heptanol, a reversible inhibitor of gap junctions, at low (0.16 mM) and high (0.5 mM) concentration as perfusate for 18 Langendorff-perfused rabbit hearts to study its effects on myocardial electrical and mechanical functions. Optical mapping was performed to measure conduction velocity (CV) and action potential duration (APD). Ultrasonic integrated backscatter and Doppler tissue imaging (DTI) were used to evaluate the intrinsic and global myocardial contractile performance. The CV decreased during low-dose heptanol infusion and became much slower at high dose (high dose vs. baseline, 50.8 +/- 10.2 cm/s vs. 69.3 +/- 8.8 cm/s, p < 0.001). After washout of heptanol, CV completely recovered. The alterations of APD by heptanol infusion were similar to CV. The APD dispersion, standard deviation of APD(80), was increased after heptanol infusion (low dose vs. baseline, 5.9 +/- 1.1 ms vs. 4.3 +/- 1.1 ms, p = 0.004; high dose, 6.0 +/- 1.3 ms, vs. baseline, p = 0.035). However, washout did not restore the APD dispersion which became even larger after washout (13.6 +/- 1.9 ms vs. high dose and baseline, both p < 0.001). Regarding contractile function, heptanol treatment resulted in a progressive decrease of cardiac cycle-dependent variations of integrated backscatter (CVIBS; low dose vs. baseline, 6.1 +/- 1.7 dB vs. 7.2 +/- 1.8 dB, p = 0.007; high dose 1.7 +/- 0.3 dB vs. baseline, p < 0.001) and peak systolic strain rate (low dose vs. baseline, -1.5 +/- 0.6 1/s vs. -1.9 +/- 0.6 1/s, p = 0.014; high dose -0.4 +/- 0.2 1/s; vs. baseline, p < 0.001). That both CVIBS and strain rate incompletely recovered after heptanol washout may be attributed to the increased APD dispersion. In conclusion, uncoupling of gap junctions resulted in slowing CV, increased repolarization heterogeneity, reduced CVIBS and impaired myocardial contractility. There was a reversible dose-response relationship between the myocardial electromechanical functions and gap junction coupling.

Rod-shaped nanocrystals elicit neuronal activity in vivo

The development of novel nanomaterials has raised great interest in efforts to evaluate their effect on biological systems, ranging from single cells to whole animals. In particular, there exists an open question regarding whether nanoparticles per se can elicit biological responses, which could interfere with the phenomena they are intended to measure. Here it is reported that challenging the small cnidaria Hydra vulgaris in vivo with rod-shaped semiconductor nanoparticles, also known as quantum rods (QRs), results in an unexpected tentacle-writhing behavior, which is Ca(2+) dependent and relies on the presence of tentacle neurons. Due to the absence of surface functionalization of the QRs with specific ligands, and considering that spherical nanoparticles with same composition as the QRs fail to induce any in vivo behavior on the same experimental model, it is suggested that unique shape-tunable electrical properties of the QRs may account for the neuronal stimulation. This model system may represent a widely applicable tool for screening neuronal response to nanoparticles in vivo.

Effects of heptanol and carbenoxolone on noradrenaline induced contractions in guinea pig vas deferens

We examined the effects of two putative gap junction blockers, heptanol and carbenoxolone, on noradrenaline-induced contractions in guinea pig vas deferens. The force generated due to the exogenously added noradrenaline (20 microM) consisted of two components: the tonic and the oscillatory. 2 mM heptanol abolished the oscillatory contractions and drastically suppressed both the maximum force (by 85.4 +/- 18.2%) as well as the tonic component (by 28.8 +/- 5.1%) (P<0.01, n=7). However, the effects of carbenoxolone (50 microM) were strikingly different, with the spikes of the oscillatory component being merged into a steady, "fused" contraction, without affecting the maximum force developed. The L-type Ca(2+) channel blocker nifedipine (2 microM) abolished the oscillatory component of the contractions and significantly reduced the maximum force and tonic component (by 82.4 +/- 6.8% and 19.7 +/- 6.4% respectively; P<0.01, n=4), in a manner similar to that elicited by heptanol. Our results indicate that (i) while carbenoxolone specifically blocks gap junctions, heptanol appears to exert its actions through non-gap junctional mechanisms, possibly by blocking VGCCs in smooth muscle; (ii) gap junctions play a significant modulatory role in the generation of noradrenaline-induced contractions in guinea pig vas deferens, particularly in the emergence of oscillatory contractions, while the maximum force developed may be independent of gap junctional contribution.

Electron microprobe analysis of rabbit ciliary epithelium indicates enhanced secretion posteriorly and enhanced absorption anteriorly

The rate of aqueous humor formation sequentially across the pigmented (PE) and nonpigmented (NPE) ciliary epithelial cell layers may not be uniform over the epithelial surface. Because of the tissue's small size and complex geometry, this possibility cannot be readily tested by conventional techniques. Rabbit iris-ciliary bodies were divided, incubated, quick-frozen, cryosectioned, and freeze-dried for electron probe X-ray microanalysis of the elemental contents of the PE and NPE cells. We confirmed that preincubation with ouabain to block Na(+),K(+)-ATPase increases Na(+) and decreases K(+) contents far more anteriorly than posteriorly. The anterior and posterior regions were the iridial portion of the primary ciliary processes and the pars plicata, respectively. Following interruption of gap junctions with heptanol, ouabain produced smaller changes in anterior PE cells, possibly reflecting higher Na(+) or K(+) permeability of anterior NPE cells. Inhibiting Na(+) entry selectively with amiloride, benzamil, or dimethylamiloride reduced anterior effects of ouabain by approximately 50%. Regional dependence of net secretion was also assessed with hypotonic stress, which stimulates ciliary epithelial cell regulatory volume decrease (RVD) and net Cl(-) secretion. In contrast to ouabain's actions, the RVD was far more marked posteriorly than anteriorly. These results suggest that 1) enhanced Na(+) reabsorption anteriorly, likely through Na(+) channels and Na(+)/H(+) exchange, mediates the regional dependence of ouabain's actions; and 2) secretion may proceed primarily posteriorly, with secondary processing and reabsorption anteriorly. Stimulation of anterior reabsorption might provide a novel strategy for reducing net secretion.

Are gap junctions truly involved in inhibitory neuromuscular interaction in mouse proximal colon?

1. Gap junctions exist between circular muscle cells of the colon and between interstitial cells of Cajal (ICC) in the myenteric plexus of the gastrointestinal tract. They also probably couple intramuscular ICC with smooth muscle cells. Recent functional evidence for this was found in dye-coupling and myoelectrical experiments. 2. In the present study, we tested the hypothesis of gap junctions putatively being involved in neuromuscular interaction in mouse colon by using different classes of gap junction blockers. 3. Electrical field stimulation of the myenteric plexus elicited tetrodotoxin-sensitive and hexamethonium-independent fast and slow inhibitory junction potentials (fIJP and sIJP, respectively) in circular smooth muscle cells, as evaluated by intracellular recording techniques in impaled smooth muscle cells. Heptanol produced a time-dependent hyperpolarization of the membrane potential (MP) and abolished fIJP and sIJP. Octanol had no effect on the MP and abolished fIJP and sIJP. Carbenoxolone produced a time-dependent depolarization of the MP without any effect on fIJP or sIJP. The connexin 43 mimetic gap junction blocker GAP-27 had no effect on MP, fIJP or sIJP. 4. Based on the presently available gap junction blockers we found no evidence that gap junctions are involved in neuromuscular transmission in mouse colon, as suggested by morphological studies.

Evidence of intercellular coupling between co-cultured adult rabbit ventricular myocytes and myofibroblasts

Intercellular coupling between ventricular myocytes and myofibroblasts was studied by co-culturing adult rabbit ventricular myocytes with previously prepared layers of cardiac myofibroblasts. Intercellular coupling was examined by: (i) tracking the movement of the fluorescent dye calcein; (ii) immunostaining for connexin 43 (Cx43); and (iii) measurement of intracellular [Ca2+] ([Ca2+]i). The effects of stimulating ventricular myocytes on the underlying myofibroblasts was examined by confocal measurements of [Ca2+]i using fluo-3. When ventricular myocytes were preloaded with calcein and co-cultured with myofibroblasts for 24 h, calcein fluorescence was detected in 52+/-4% (n=8 co-cultures) of surrounding myofibroblasts. Treatment with the gap junction uncoupler heptanol significantly reduced the movement of calcein (12+/-3%, n=6 co-cultures). Immunostaining showed expression of Cx43 in co-cultured myofibroblasts and myocytes. Field stimulation of ventricular myocytes co-cultured with myofibroblasts increased myofibroblast [Ca2+]i, no response was observed after treatment with heptanol or stimulation of fibroblasts in the absence of ventricular myocytes. Action potential parameters of ventricular myocytes in co-culture were similar to control values. However, application of the hormone sphingosine-1-phosphate (S-1-P) to the co-culture caused a depolarization of ventricular myocytes to approximately -20 mV. Sphingosine-1-phosphate had no effect on ventricular myocytes alone. Voltage-clamp measurements of isolated myofibroblasts indicated that S-1-P activated a significant quasi-linear current with a reversal potential of approximately -40 mV. In conclusion, this study shows that stimulation of the ventricular myocyte influences the intracellular Ca2+ of the linked myofibroblast via connexons. These intercellular links also allow the myofibroblasts to influence the electrical activity of the myocyte. This work indicates the nature of the gap junction-mediated bi-directional interactions that occur between ventricular myocyte and myofibroblast.

Chloride secretion by porcine ciliary epithelium: New insight into species similarities and differences in aqueous humor formation

PURPOSE

To investigate the electrophysiology and mechanisms of chloride (Cl-) transport across the ciliary body-epithelium (CBE) of the porcine eye. The pig is widely believed to be a good model for studying human physiology. Current results strengthen our understanding of the physiology of aqueous humor formation (AHF).

METHODS

Freshly isolated porcine CBE were maintained in modified Ussing-Zerahn-type chambers. The effects of the bathing anion substitution (Cl- and HCO3-) and transport inhibitors including bumetanide, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt (DIDS), heptanol, and two chloride channel inhibitors, 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), and niflumic acid, on the electrical properties and transepithelial Cl- transport were investigated.

RESULTS

Viable porcine CBE preparations were maintained in vitro. A spontaneous transepithelial potential difference (PD) of approximately 1 mV was found across the CBE (aqueous side negative). The magnitudes of the PD and short-circuit current (I(sc)) were found to be dependent on both the bathing Cl- and HCO3- concentrations. In short-circuited conditions, a significant net Cl- transport (1.01 microEq x h(-1) x cm(-2); n = 109; P < 0.001) in the stromal-to-aqueous direction (J(net)Cl) was detected. The magnitude of the Cl- current carried by the J(net)Cl was approximately 2.2 times the measured I(sc), suggesting there was cation (e.g., Na+) transport along with Cl- and/or anion transport (e.g., HCO3-) in the opposite direction. Bilateral bumetanide (0.1 mM) reduced the J(net)Cl by approximately 56% while stromal DIDS (0.1 mM) produced no inhibition. Instead, aqueous DIDS (0.1 mM) triggered a sustained stimulation of both I(sc) and J(net)Cl. Even if bilateral DIDS was used at a higher concentration (1 mM), together with bilateral dimethylamiloride (DMA, 0.1 mM), no inhibition of the I(sc) was observed. Bilateral heptanol (3.5 mM) drastically reduced the I(sc) and J(net)Cl. NPPB (0.1 mM), a common chloride channel inhibitor, did not inhibit the J(net)Cl, whereas NFA (1.0 mM) virtually abolished it.

CONCLUSIONS

In the porcine eye, active secretion of Cl- into aqueous was identified that may act as a driving force for AHF. The bumetanide-sensitive Na+/K+/2Cl- cotransporter (NKCC) clearly contributes to the Cl- uptake into the pigmented epithelium (PE), whereas the DIDS-sensitive Cl-/HCO3- anion exchanger (AE) may exert a minor role. The intercellular gap junctions couple the porcine ciliary bilayers and thus the transepithelial Cl- transport, as in other species. The Cl- channel/efflux pathway located in the nonpigmented epithelium (NPE) is niflumic acid-sensitive but NPPB-insensitive. We also hypothesize that the AE located on the NPE may regulate the activity of a putative Cl- channel on the basolateral membrane facing aqueous via modulation of the intracellular pH (pHi). This work reinforces the general consensus that active secretion of Cl- is the major driving force of AHF in mammalian eye and further substantiates the existence of species differences in the mechanism that accomplishes transepithelial Cl- transport.

Albumin-bound lipids induce free cytoplasmic calcium oscillations in human osteoblast-like cells

[Ca(2+)](i) oscillations were found in human osteoblast-like cells (hOB cells) exposed to high-lipid bovine serum albumin (BSA), but not when exposed to low-lipid BSA. These [Ca(2+)](i) oscillations were inhibited by heptanol and suramin, which implies that gap junctions and purinergic signalling may be important for these [Ca(2+)](i) oscillations. The high-lipid BSA preparation that was used contains arachidonic acid. [Ca(2+)](i) oscillations could be induced by low lipid albumin with arachidonic acid added. The albumin-bound lipids were also important for osteoblast growth since DNA synthesis and the total cell protein content was higher in hOB cells exposed to high-lipid BSA. The effect of arachidonic acid on hOB cell proliferation was bone-donor dependent; both stimulatory and inhibitory effects were observed. The physiological importance of albumin-bound lipids is unclear; given that albumin has only minimal contact with osteoblasts under normal conditions. Only when bone capillaries are disrupted, e.g. during a fracture, would significant amounts of albumin reach osteoblasts. Albumin-bound lipids could therefore contribute to stimulation of osteoblast proliferation during fracture healing.

Carbenoxolone and mefloquine suppress tremor in the harmaline mouse model of essential tremor

Excessive olivo-cerebellar synchrony is implicated in essential tremor. Because synchrony in some networks is mediated by gap junctions, we examined whether the gap junction blockers heptanol, octanol, carbenoxolone, and mefloquine suppress tremor in the mouse harmaline model, and performed an open-treatment clinical study of mefloquine for essential tremor. Digitized motion was used to quantify tremor in mice administered harmaline, 20 mg/kg s.c. In mice the broad-spectrum gap junction blockers heptanol, octanol (350 mg/kg i.p. each), and carbenoxolone (20 mg/kg) suppressed harmaline tremor. Mefloquine (50 mg/kg), which blocks gap junctions containing connexin 36, robustly suppressed harmaline tremor. Glycyrrhizic acid (related to carbenoxolone) and chloroquine (related to mefloquine), which do not block gap junctions, failed to suppress harmaline tremor in mice. Clinically, tremor was assessed with standard rating scales, and subjects asked to take 62.5, 125, and 250 mg mefloquine weekly for 12 weeks at each dose. None of the four human subjects showed a meaningful tremor reduction with mefloquine, likely because clinical levels were below those required for efficacy. In view of recent genetic evidence, the anti-tremor mechanism of these compounds is uncertain but may represent a novel therapeutic target, possibly involving gap junctions other than those containing connexin 36.

Effect of heptanol on noradrenaline-induced contractions in rat vas deferens

We have studied the effects of 1-heptanol and nifedipine on noradrenaline (NA)-induced contractions in order to explore the role of gap junctions and their interactions with L-type Ca2+ channel mediated [Ca2+]o entry in the generation of NA-induced contractions in the rat vas deferens. Application of 20 microM NA to rat vas deferens resulted in contractions with three different components, an initial phasic component followed by a tonic component overlapped with an oscillatory component. Heptanol (0.01-2 mM) induced a concentration dependent reduction of the contractions. 2 mM heptanol reduced the phasic component by 32.9 +/- 4.4% and the tonic component by 93.8 +/- 1.9% of control, while the oscillatory component was completely abolished (n=7). Nifedipine (2 microM) reduced the phasic component by 34.5 +/- 4.1% and the tonic component by 89.5 +/- 3.8% of control and abolished the oscillatory component (n=6). In the presence of heptanol and nifedipine together, the phasic component was reduced by 61.3 +/- 8.3% and the tonic component by 94.5 +/- 1.0% of control. The oscillatory component was completely abolished (n=6). These results allow the conclusion that phasic contraction is mainly due to the direct action of NA, independent of gap junctions, while the tonic and oscillatory contractions may depend significantly on cell-to-cell communication. These in turn may depend critically on the availability of extracellularly derived Ca2+.

Effect of gap junction uncoupler heptanol on resistance arteries reactivity in experimental models of diabetes, hyperlipemia and hyperlipemia-diabetes

The understanding of the involvement of the gap junctions (GJ) in the vascular reactivity is an ongoing effort. In this study we questioned on impact of pathologies such as diabetes, hyperlipemia, and simultaneous hyperlipemia-diabetes on GJ involvement in the contractile/relaxant response of the mesenteric resistance arteries. To this purpose, four groups of Golden Syrian hamsters were used: (i) diabetics (D), injected by streptozotocin, (ii) hyperlipemics (H), fed the standard chow of the species supplemented with 3% cholesterol and 15% butter, (iii) simultaneously hyperlipemic-diabetics (HD), and (iv) controls (C), age-matched normal healthy animals. At 24 weeks after the beginning of the experiment, the vascular reactivity of the resistance arteries was measured by the myograph technique in the presence/absence of 1 mM Heptanol (Hep) and of vasoconstrictors and vasodilators. The results showed that: (i) in pathological conditions 1 mM Hep significantly impaired the constrictor response of the hamster resistance arteries to both 10(-5) M NA (noradrenaline, agonist of alpha(1)-adrenoceptors) and 64.1 mM K+ (potassium ion, the major intracellular cation). The impairment occur in the group range: HD < H < D < C being the highest at the simultaneous insult of hyperlipemia and diabetes; (ii) independently of the pathological condition, 1 mM Hep abolishes both endothelium-dependent and independent relaxation of the hamster resistance arteries. At 1 mM Hep we noticed a reversible effect on endothelium-dependent relaxation that may be partially restored (in normal) in the presence of L-arginine. It is hoped that these results may contribute to understanding of the involvement of GJ in vascular pathology/dysfunction.

Pathophysiological basis for monitoring of whole heart conductance by 2-lead system

BACKGROUND

The defibrillation threshold (DFT) is elevated during myocardial ischemia, but the underlying mechanism remains to be elucidated. The hypothesis tested by the present study was that whole heart conductance (WHC) is a determinant of DFT.

METHODS AND RESULTS

WHC was monitored across the longest diameter of the isolated perfused rat heart, using a 2-electrode instrument under various conditions including ischemia-reperfusion (IR). In the control study, WHC was influenced by the conductivity and flow rate of the solution. In IR, WHC decreased immediately after the onset of perfusion arrest in a single exponential manner, then declined again gradually. The second decrease was augmented and accelerated by pretreatment with 1.0 mmol/L heptanol (p<0.005) or high-[Ca2+]e (p<0.001), and was attenuated and delayed by pretreatment with 1.0 micromol/L verapamil (p<0.01). WHC after reperfusion was greater than the pre ischemic level. The postischemic increase in WHC was proportional to the ischemic interval and tissue water content as assessed by desiccation method.

CONCLUSION

Although time-dependent alterations in DFT in ischemic hearts may be attributable at least in part to dynamic changes in WHC, WHC should be interpreted carefully because it reflects many physiological factors such as coronary perfusion, electrical coupling of cardiac myocytes and tissue edema.

Protective effect of gap junction uncouplers given during hypoxia against reoxygenation injury in isolated rat hearts

It has been shown that cell-to-cell chemical coupling may persist during severe myocardial hypoxia or ischemia. We aimed to analyze the effects of different, chemically unrelated gap junction uncouplers on the progression of ischemic injury in hypoxic myocardium. First, we analyzed the effects of heptanol, 18α-glycyrrhetinic acid, and palmitoleic acid on intracellular Ca2+ concentration during simulated hypoxia (2 mM NaCN) in isolated cardiomyocytes. Next, we analyzed their effects on developed and diastolic tension and electrical impedance in 47 isolated rat hearts submitted to 40 min of hypoxia and reoxygenation. All treatments were applied only during the hypoxic period. Cell injury was determined by lactate dehydrogenase (LDH) release. Heptanol, but not 18α-glycyrrhetinic acid nor palmitoleic acid, attenuated the increase in cytosolic Ca2+ concentration induced by simulated ischemia in cardiomyocytes and delayed rigor development (rigor onset at 7.31 ± 0.71 min in controls vs. 14.76 ± 1.44 in heptanol-treated hearts, P < 0.001) and the onset of the marked changes in electrical impedance (tissue resistivity: 4.02 ± 0.29 vs. 7.75 ± 1.84 min, P = 0.016) in hypoxic rat hearts. LDH release from hypoxic hearts was minimal and was not significantly modified by drugs. However, all gap junction uncouplers, given during hypoxia, attenuated LDH release during subsequent reoxygenation. Dose-response analysis showed that increasing heptanol concentration beyond the level associated with maximal effects on cell coupling resulted in further protection against hypoxic injury. In conclusion, gap junction uncoupling during hypoxia has a protective effect on cell death occurring upon subsequent reoxygenation, and heptanol has, in addition, a marked protective effect independent of its uncoupling actions.

The hyperfluidization of mammalian cell membranes acts as a signal to initiate the heat shock protein response

The concentrations of two structurally distinct membrane fluidizers, the local anesthetic benzyl alcohol (BA) and heptanol (HE), were used at concentrations so that their addition to K562 cells caused identical increases in the level of plasma membrane fluidity as tested by 1,6-diphenyl-1,3,5-hexatriene (DPH) anisotropy. The level of membrane fluidization induced by the chemical agents on isolated membranes at such concentrations corresponded to the membrane fluidity increase seen during a thermal shift up to 42 degrees C. The formation of isofluid membrane states in response to the administration of BA or HE resulted in almost identical downshifts in the temperature thresholds of the heat shock response, accompanied by increases in the expression of genes for stress proteins such as heat shock protein (HSP)-70 at the physiological temperature. Similarly to thermal stress, the exposure of the cells to these membrane fluidizers elicited nearly identical increases of cytosolic Ca2+ concentration in both Ca2+-containing and Ca2+-free media and also closely similar extents of increase in mitochondrial hyperpolarization. We obtained no evidence that the activation of heat shock protein expression by membrane fluidizers is induced by a protein-unfolding signal. We suggest, that the increase of fluidity in specific membrane domains, together with subsequent alterations in key cellular events are converted into signal(s) leading to activation of heat shock genes.

Heterogeneous response of microvascular endothelial cells to shear stress

We investigated changes in calcium concentration in cultured bovine aortic endothelial cells (BAECs) and rat adrenomedulary endothelial cells (RAMECs, microvascular) in response to different levels of shear stress. In BAECs, the onset of shear stress elicited a transient increase in intracellular calcium concentration that was spatially uniform, synchronous, and dose dependent. In contrast, the response of RAMECs was heterogeneous in time and space. Shear stress induced calcium waves that originated from one or several cells and propagated to neighboring cells. The number and size of the responding groups of cells did not depend on the magnitude of shear stress or the magnitude of the calcium change in the responding cells. The initiation and the propagation of calcium waves in RAMECs were significantly suppressed under conditions in which either purinergic receptors were blocked by suramin or extracellular ATP was degraded by apyrase. Exogenously applied ATP produced similarly heterogeneous responses. The number of responding cells was dependent on ATP concentration, but the magnitude of the calcium change was not. Our data suggest that shear stress stimulates RAMECs to release ATP, causing the increase in intracellular calcium concentration via purinergic receptors in cells that are heterogeneously sensitive to ATP. The propagation of the calcium signal is also mediated by ATP, and the spatial pattern suggests a locally elevated ATP concentration in the vicinity of the initially responding cells.

Effects of Heptanol on Neurogenic Contractions of Vas Deferens: A Comparative Study of Stimulation Frequency in Guinea Pig and Rat

This study examines the role of gap junctional communication in smooth muscle in relation to the frequency of stimulation and the innervation density of the tissue in the generation of neurogenic contractions. Toward this end the effects of heptanol, a gap junctional blocker, on the neurogenic contractions of guinea pig and rat vas deferens at different frequencies of stimulation (single pulse, 5, 10, 20, 40, 60, and 80 Hz) were studied. In both the prostatic and epididymal halves of these tissues, heptanol abolished the neurogenic contractions at the lower frequencies of stimulation. At higher frequencies, contractions were resistant to heptanol action. The effect of heptanol on the neurogenic contractions was found to decrease with increasing stimulation frequency. The neurogenic contractions of rat vas deferens were more resistant to heptanol than those of guinea pig vas deferens. Our data indicate that gap junctional communication is significant in the generation of neurogenic contractions in both guinea pig and rat vas deferens in a frequency-dependent manner, and we discuss the mechanisms underlying these findings.

Gap Junction-Mediated Intercellular Communication between Dendritic Cells (DCs) Is Required for Effective Activation of DCs

Gap junctions, formed by members of the connexin (Cx) family, are intercellular channels allowing direct exchange of signaling molecules. Gap junction-mediated intercellular communication (GJIC) is a widespread mechanism for homeostasis in organs. GJIC in the immune system is not yet fully understood. Although dendritic cells (DC) reportedly form cell-to-cell contact between DCs in nonlymphoid and lymphoid organs, GJIC between DCs remains unknown. In this study we examined whether DCs form GJIC. XS52 and bone marrow-derived DCs (BMDCs) were tested for GJIC by counting intercellular transfer of Lucifer Yellow microinjected into a cell. Either DC became effectively dye-coupled when activated with LPS plus IFN-gamma or TNF-alpha plus IFN-gamma. LPS- plus IFN-gamma-induced dye-coupling was mediated by DC-derived TNF-alpha. In addition, CpG plus IFN-gamma induced dye-coupling in BMDCs, which was also mediated by DC-derived TNF-alpha. LPS- plus IFN-gamma-induced activation of DCs (assessed by CD40 expression) was observed when there was cell-to-cell contact and was significantly blocked by heptanol, a gap junction blocker. These results indicate that cell-to-cell contact and GJIC are required for effective DC activation. In addition, heptanol significantly inhibited the LPS- plus IFN-gamma-induced up-regulation of the other costimulatory (i.e., CD80 and CD86) and MHC class II molecules expressed by BMDCs, and it significantly reduced their allostimulatory capacity. Among Cx members, Cx43 was up-regulated in dye-coupled BMDCs, and Cx mimetic peptide, a blocker of Cx-mediated GJIC, significantly inhibited the dye-coupling and activation, suggesting the involvement of Cx43. Thus, our study provides the first evidence for GJIC between DCs, which is required for effective DC activation.

Isolated primary osteocytes express functional gap junctions in vitro

The osteocyte is the most abundant cell type in bone and is embedded in mineralized bone matrix. Osteocytes are still poorly characterized because of their location and the lack of primary osteocyte isolation methods. Data on the cell biology of osteocytes is especially limited. We have isolated primary osteocytes from rat cortical bone by applying repeated enzymatic digestion and decalcification. The isolated osteocytes expressed typical osteocytic morphology with cell-cell contacts via long protrusions after a 1-day culture. These cells were negative or faintly positive for alkaline phosphatase but expressed high levels of osteocalcin, PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome), and DMP1 (dentin matrix protein 1). These cells also revealed patchy membrane staining for connexin43. For studying the function of gap junctions in isolated osteocytes, we microinjected rhodamine-labeled dextran (MW: 10,000) and Lucifer yellow (MW: 457) and found that Lucifer yellow was rapidly transmitted to several surrounding cells, whereas dextran remained in the injected cells. Heptanol and 18alpha-glycyrrhetinic acid inhibited the transfer of Lucifer yellow. This clearly showed the existence of functional gap junctions in cultured osteocytes. Enveloped viruses, such as vesicular stomatitis virus and influenza A virus, were used for studying cell polarity. We were unable to demonstrate plasma membrane polarization with enveloped viruses in isolated primary osteocytes in culture. Our results suggest that osteocytes do not possess apical and basolateral plasma membrane domains as do osteoblasts, which are their precursors.

DELAYED UNCOUPLING CONTRIBUTES TO THE PROTECTIVE EFFECT OF HEPTANOL AGAINST ISCHAEMIA IN THE RAT ISOLATED HEART

1. It is known that infusion of the gap junction uncoupler heptanol, before ischaemia or during reperfusion, limits myocardial infarct size. However, whether this cardiac effect is linked to the effect of heptanol on communication across gap junctions has not been elucidated. The aims of the present study were to examine the effect of heptanol on infarct size, arrhythmias and myocardial tissue resistance and to assess whether changes in electrical coupling correlate with cardiac protection. 2. Rat isolated, perfused hearts were subjected to a 24 min infusion of heptanol (0.05, 0.1, 0.5 or 1.0 mmol/L) followed by 20 min regional ischaemia and 60 min reperfusion, or by 70 min global no-flow ischaemia. The effective refractory period, action potential and conduction velocity were measured in papillary muscles from the right ventricle. Heptanol markedly decreased arrhythmia scores during ischaemia and reperfusion, as well as reducing infarct size to a degree similar to that induced by ischaemic preconditioning. In the prolonged ischaemia model, heptanol delayed the onset of uncoupling, increased time to plateau and decreased the maximal rate of uncoupling during ischaemia. Ischaemic preconditioning had similar effects on these parameters. In papillary muscle, heptanol reduced the conduction velocity of the action potential in a dose-dependent manner, but had no significant effect on resting potential, action potential amplitude, action potential duration, maximal upstroke of depolarization or effective refractory period. 3. These results demonstrate that treatment with the gap junction uncoupler heptanol confers cardioprotection against ischaemia and this effect is related to delayed electrical uncoupling during prolonged ischaemia.

[The effect of gap blocker 1-heptanol on function and morphology of guinea pig cochlea]

OBJECTIVE

To investigate the role of gap junctions in hearing function of guinea pig in vivo.

METHOD

Seven guinea pigs were inoculated with 1-heptanol into perilymphatic space after a small hole was drilled in the bony wall near tympanic scala of the base turn. Auditory brainstem response (ABR) was recorded before, 30 min, 60 min, 90 min 120 min after operation. Two hours after surgery, all the animals were killed and the ultrastructure of guinea cochlea was observed by making electron microscopy specimens.

RESULT

The application of 1-heptanol into guinea pig cochlea resulted in large increase in ABR threshold, which showed 30 to 40 dB elevation in guinea pig. And 1-heptanol could destroy the gap conjunction structure between hair cells and Deiter's cells in guinea cochlea.

CONCLUSION

The gap blocker 1-heptanol might significantly influence the guinea pig's hearing function, and the gap conjunction might play an important role in normal cochlear function and K+ recycle in inner ear of guinea pig.

Cells of Candida utilis for in vitro (R)-phenylacetylcarbinol production in an aqueous/octanol two-phase reactor

(R)-Phenylacetylcarbinol (PAC), a pharmaceutical precursor, was produced from benzaldehyde and pyruvate by pyruvate decarboxylase (PDC) of Candida utilis in an aqueous/organic two-phase emulsion reactor. When the partially purified enzyme in this previously established in vitro process was replaced with C. utilis cells and the temperature was increased from 4 to 21 degrees C, a screen of several 1-alcohols (C4-C9) confirmed the suitability of 1-octanol as the organic phase. Benzyl alcohol, the major by-product in the commercial in vivo conversion of benzaldehyde and sugar to PAC by Saccharomyces cerevisiae, was not formed. With a phase volume ratio of 1:1 and 5.6 g C. utilis l-1 (PDC activity 2.5 U ml-1), PAC levels of 103 g l-1 in the octanol phase and 12.8 g l-1 in the aqueous phase were produced in 15 h at 21 degrees C. In comparison to our previously published process with partially purified PDC in an aqueous/octanol emulsion at 4 degrees C, PAC was produced at a 4-times increased specific rate (1.54 versus 0.39 mg U-1 h-1) with simplified catalyst production and reduced cooling cost. Compared to traditional in vivo whole cell PAC production, the yield on benzaldehyde was 26% higher, the product concentration increased 3.9-fold (or 6.9-fold based on the organic phase), the productivity improved 3.1-fold (3.9 g l-1 h-1) and the catalyst was 6.9-fold more efficient (PAC/dry cell mass 10.3 g g-1).

The effect of extracellular calcium concentration on calcium-mediated cell signaling in NF1 tumor suppressor-deficient keratinocytes

Capacitative calcium entry and calcium wave propagation were studied in keratinocytes from healthy volunteers and patients with type 1 neurofibromatosis (NF1) in calcium-depleted and in low calcium culture medium. In previous studies, we found evidence that mutations of the NF1 tumor suppressor gene can lead to altered calcium-mediated cell signaling in keratinocytes cultured in the presence of a high extracellular calcium concentration. The present study demonstrated that the differences between normal and NF1 keratinocytes were dependent on extracellular calcium concentration. Specifically, when keratinocytes were exposed to thapsigargin under calcium-depleted culture conditions the subsequent increase in free intracellular calcium concentration was moderate in NF1 keratinocytes compared to controls. The finding indicates lowered endoplasmic calcium stores in NF1 which may also in part explain the reduced activation signal for capacitative calcium influx and the wound-induced intracellular Ca2+ transient observed in NF1 keratinocytes maintained in culture medium containing 0.05 mM calcium. The differences between control and NF1 keratinocytes were most pronounced when the cells were cultured in the presence of a high (1.8 mM) calcium concentration. Since elevated extracellular calcium levels induce keratinocytes to form cellular contacts and lead to terminal differentiation, markedly aberrant responses of NF1 keratinocytes in the presence of a high calcium concentration may help to explain previous findings on impaired formation of cellular junctions and differentiation in NF1 deficient cells.

Insulin-like growth factor-I induces oocyte maturational competence but not meiotic resumption in white bass (Morone chrysops) follicles in vitro: evidence for rapid evolution of insulin-like growth factor action

A combination of recombinant human (rh) insulin-like growth factor-I (IGF-I) (25 nM) and the maturation-inducing hormone (MIH), 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S; 72.5 nM), induced germinal vesicle breakdown (GVBD) in ovarian follicles of white bass incubated in vitro, whereas a four times greater concentration of each hormone was ineffective alone. These results indicate that IGF-I induces oocyte maturational competence (OMC) but not meiotic resumption in white bass. Culture medium concentrations of 20beta-S remained below detection limits for ovarian fragments incubated with rhIGF-I. Actinomycin D blocked GVBD in response to hCG but not to rhIGF-I plus 20beta-S, suggesting that IGF-I requires de novo translation but not transcription to induce OMC. Gap junction uncouplers, 1-octanol and 1-heptanol, and the phosphatidylinositiol 3-kinase (PI 3-K) inhibitors, wortmannin and LY 294002, attenuated hCG-, 20beta-S-, and rhIGF-I plus 20beta-S-induced GVBD. Although these inhibitors reduced hCG-induced progestin release, PI 3-K inhibitors did not alter MIH synthesis in some incubations and addition of 20beta-S to the incubations did not fully overcome the effects of either class of inhibitors, suggesting that decreasing MIH production is not their only inhibitory effect on gonadotropin (GtH) action. Our data suggest that gap junctions and PI 3-K activity are necessary for GtH and IGF-I to induce and maintain OMC in white bass. The induction of OMC but not meiotic resumption by IGF-I in white bass, compared with the induction of meiotic resumption but not OMC by IGF-I discovered in the congeneric striped bass suggests rapid evolution of the reproductive actions of IGF-I among temperate basses (genus Morone).

Endocochlear potential and endolymphatic K+ changes induced by gap junction blockers

OBJECTIVE

To examine the effects of gap junction blockers on the endocochlear potential (EP) and endolymphatic potassium concentration ([K(+)](e)).

MATERIAL AND METHODS

The EP and [K(+)](e) were monitored using double-barreled ion-selective microelectrodes in the second turn of the guinea pig cochlea during perilymphatic perfusion.

RESULTS

When the perilymphatic scalae of the cochlea were perfused with artificial perilymph containing 10 mM n-heptanol the EP was decreased by -8.8+/-1.4 mV (n=10), and this was accompanied by a decline in the [K(+)](e) of -6.7+/-2.1 mM (n=6). Perilymphatic application of 10 mM hexanol also produced declines in both the EP and [K(+)](e). In control studies, perilymphatic perfusion with 10 mM ethanol showed no remarkable changes in either the EP or [K(+)](e). Anoxia during perfusion with heptanol resulted in the generation of a negative EP, similar to the situation in controls.

CONCLUSIONS

A decline in the EP together with a lowering of [K(+)](e) induced by long-chain n-alkanols, which act as gap junction blockers, may be explained by an interruption in potassium ion transport related to a gap junction dysfunction.

Coupling between sensory neurons in the olfactory epithelium

Coupling of olfactory sensory neurons (OSNs) in the olfactory epithelium of Necturus maculosus was demonstrated by dye-transfer with Lucifer yellow CH; however, the incidence of dye-transfer was low. Immunocytochemistry and Western blot analysis indicated that connexin 43, a gap junction channel subunit, was widely expressed by cells in the olfactory epithelium. Electrical coupling by presumptive gap junctions was assessed using electrophysiological recordings, heptanol block, tracer-uptake through hemi-junctions, and tracer-injection into tissue whole-mounts. Coupling, which involved pairs of OSNs only, was detected in approximately 3-10% of the OSN population; there was no evidence that OSNs were coupled into extended neural syncitia. These results suggest that coupling of OSNs by gap junctions is unlikely to have a general role in olfactory responses by mature (odor responsive) OSNs. Instead, the incidence of inter-neuronal coupling was small, similar to the fraction of immature OSNs, suggesting a possible role of gap junctions in the continual turnover and development of OSNs or possibly their senescence.

In vivo time-lapse imaging in medaka – n-heptanol blocks contractile rhythmical movements

Medaka is an ideal model system for developmental studies as it combines the advantages of powerful genetics and classical embryology. Due to the accessibility, transparency and fast development, embryogenesis and morphogenesis can be followed in vivo. Microscopic time-lapse imaging, however, requires the immobilization of the object to be observed. In medaka rhythmical contractile movements of the blastoderm during early development hampered time-lapse studies, as they cause the embryo to rotate vividly. Here we show that the contractile movements can be reduced by continuous treatment with the gap-junction uncoupling agent n-heptanol up to the 12-somite stage (stage 23) without interfering with development. This allows for the first time to perform high-resolution time-lapse studies in medaka.

Enhanced effect of gap junction uncouplers on macroscopic electrical properties of reperfused myocardium

Transient inhibition of gap junction (GJ)-mediated communication with heptanol during myocardial reperfusion limits infarct size. However, inhibition of cell coupling in normal myocardium may be arrhythmogenic. The purpose of this study was to test the hypothesis that the consequences of GJ inhibition may be magnified in reperfused myocardium compared with normal tissue, thus allowing the inhibition of GJs in reperfused tissue while only minimally modifying overall macroscopic cell coupling in normal myocardium. Concentration-response curves were defined for the effects of heptanol, 18alpha-glycyrrhetinic acid, halothane, and palmitoleic acid on conduction velocity, tissue electrical impedance, developed tension and lactate dehydrogenase (LDH) release in normoxically perfused rat hearts (n= 17). Concentrations lacking significant effects on tissue impedance were added during the initial 15 min of reperfusion in hearts submitted to 60 min (n= 43) or 30 min (n= 35) of ischaemia. These concentrations markedly increased myocardial electrical impedance (resistivity and phase angle) in myocardium reperfused after either 30 or 60 min of ischaemia, and reduced reperfusion-induced LDH release after 1 h of ischaemia by 83.6, 57.9, 51.7 and 52.5% for heptanol, 18alpha-glycyrrhetinic acid, halothane and palmitoleic acid, respectively. LDH release was minimal in hearts submitted to 30 min of ischaemia, independently of group allocation. In conclusion, the present results strongly support the hypothesis that intercellular communication in postischaemic myocardium may be effectively reduced by concentrations of GJ inhibitors affecting only minimally overall electrical impedance in normal myocardium. Reduction of cell coupling during initial reperfusion was consistently associated with attenuated lethal reperfusion injury.

Junctional and nonjunctional effects of heptanol and glycyrrhetinic acid derivates in rat mesenteric small arteries

1 Heptanol, 18alpha-glycyrrhetinic acid (18alphaGA) and 18beta-glycyrrhetinic acid (18betaGA) are known blockers of gap junctions, and are often used in vascular studies. However, actions unrelated to gap junction block have been repeatedly suggested in the literature for these compounds. We report here the findings from a comprehensive study of these compounds in the arterial wall. 2 Rat isolated mesenteric small arteries were studied with respect to isometric tension (myography), [Ca2+]i (Ca(2+)-sensitive dyes), membrane potential and--as a measure of intercellular coupling--input resistance (sharp intracellular glass electrodes). Also, membrane currents (patch-clamp) were measured in isolated smooth muscle cells (SMCs). Confocal imaging was used for visualisation of [Ca2+]i events in single SMCs in the arterial wall. 3 Heptanol (150 microm) activated potassium currents, hyperpolarised the membrane, inhibited the Ca2+ current, and reduced [Ca2+]i and tension, but had little effect on input resistance. Only at concentrations above 200 microm did heptanol elevate input resistance, desynchronise SMCs and abolish vasomotion. 4 18betaGA (30 microm) not only increased input resistance and desynchronised SMCs but also had nonjunctional effects on membrane currents. 18alphaGA (100 microm) had no significant effects on tension, [Ca2+]i, total membrane current and synchronisation in vascular smooth muscle. 5 We conclude that in mesenteric small arteries, heptanol and 18betaGA have important nonjunctional effects at concentrations where they have little or no effect on intercellular communication. Thus, the effects of heptanol and 18betaGA on vascular function cannot be interpreted as being caused only by effects on gap junctions. 18alphaGA apparently does not block communication between SMCs in these arteries, although an effect on myoendothelial gap junctions cannot be excluded.

[Repellent effect of volatile oil from whitefly (Syngonium podophyllum) on aphids and its chemical constituents]

The interference effect of volatile oil from whitefly (Syngonium podophyllum) on aptera aphid, guard aphid (Aphis gossypii), mustard aphid (Lipaphis erysimi) and red peach aphid (Myzus persicae) was studied by using four arms olfraetometes. The results showed that the volatile oil had distinct repelling effect. The staying periods of test aphids in test areas were obviously shorter than in control areas, and the selecting frequencies were less than the control, too. The volatile oil did not show repelling effect on red peach aphid at the test concentrations. The components of the volatile oil from S. podophyllum were analysed by GC-MS. 43 constituents were identified.

An investigation of chemotaxis in the insect parasitic nematode Heterorhabditis bacteriophora

We tested the chemotactic responses of dauer juvenile stages (DJs) of the insect parasitic nematode Heterorhabditis bacteriophora to a variety of compounds that are known to be highly attractive or highly repellent to Caenorhabditis elegans. While H. bacteriophora DJs respond to alcohols and some aromatic compounds as well as to host metabolites such as uric acid and CO2, the most notable difference in the responses of these two nematodes is that H. bacteriophora DJs are unresponsive to a large number of compounds which C. elegans finds highly attractive. The latter compounds are typical by-products of bacterial metabolism and include aldehydes, esters, ketones and short-chain alcohols. While C. elegans finds long-chain alcohols (e.g. 1-heptanol and 1-octanol) repellent and short-chain alcohols highly attractive, H. bacteriophora DJs are strongly attracted to 1-heptanol, 1-octanol and 1-nonanol and find short-chain alcohols to be only slightly attractive. Parasitic-stage H. bacteriophora nematodes show a very weak chemotactic response to volatile molecules that DJs find highly attractive. Our results suggest that, associated with the adoption of a parasitic mode of life by Heterorhabditis, there was an adaptive change in chemotactic behaviour of the infective stages, resulting in a decreased sensitivity to volatile by-products of bacterial metabolism and an increased sensitivity towards long-chain alcohols and other insect-specific volatiles and possibly also to herbivore-induced plant volatiles.

Electron microprobe analysis of ouabain-exposed ciliary epithelium: PE-NPE cell couplets form the functional units

Aqueous humor is secreted by the bilayered ciliary epithelium. Solutes and water enter the pigmented ciliary epithelial (PE) cell layer, cross gap junctions into the nonpigmented ciliary epithelial (NPE) cell layer, and are released into the aqueous humor. Electrical measurements suggest that heptanol reduces transepithelial ion movement by interrupting PE-NPE communication and that gap junctions may be a regulatory site of aqueous humor formation. Several lines of evidence also suggest that net ciliary epithelial transport is strongly region dependent. Divided rabbit iris-ciliary bodies were incubated in chambers under control and experimental conditions, quick-frozen, cryosectioned, and freeze-dried. Elemental intracellular contents of NPE and PE cells were determined by electron probe X-ray microanalysis. With or without heptanol, ouabain produced concentration- and time-dependent changes more markedly in anterior than in posterior epithelium. Without heptanol, there were considerable cell-to-cell variations in Na gain and K loss. However, contiguous NPE and PE cells displayed similar changes, even when nearby cell pairs were little changed by ouabain in aqueous, stromal, or both reservoirs. In contrast, with heptanol present, ouabain added to aqueous or both reservoirs produced much larger changes in NPE than in PE cells. The results indicate that 1) heptanol indeed interrupts PE-NPE junctions, providing an opportunity for electron microprobe analysis of the sidedness of modification of ciliary epithelial secretion; 2) Na and K undergo faster turnover in anterior than in posterior epithelium; and 3) PE-NPE gap junctions differ from PE-PE and NPE-NPE junctions in permitting ionic equilibration between adjoining ouabain-stressed cells.

Behavior of ectopic surface: effects of beta-adrenergic stimulation and uncoupling

By using both experimental and theoretical means, we have addressed the progression of ectopic activity from individual cardiac cells to a multicellular two-dimensional network. Experimental conditions that favor ectopic activity have been created by local perfusion of a small area of cardiomyocyte network (I-zone) with an isoproterenol-heptanol containing solution. The application of this solution initially slowed down and then fully blocked wave propagation inside the I-zone. After a brief lag period, ectopically active cells appeared in the I-zone, followed by evolution of the ectopic clusters into slowly propagating waves. The changing pattern of colliding and expanding ectopic waves confined to the I-zone persisted for as long as the isoproterenol-heptanol environment was present. On restoration of the control environment, the ectopic waves from the I-zone broke out into the surrounding network causing arrhythmias. The observed sequence of events was also modeled by FitzHugh-Nagumo equations and included a cell's arrangement of two adjacent square regions of 20 x 20 cells. The control zone consisted of well-connected, excitable cells, and the I-zone was made of weakly coupled cells (heptanol effect), which became spontaneously active as time evolved (isoproterenol effect). The dynamic events in the system have been studied numerically with the use of a finite difference method. Together, our experimental and computational data have revealed that the combination of low coupling, increased excitability, and spatial heterogeneity can lead to the development of ectopic waves confined to the injured network. This transient condition appears to serve as an essential step for the ectopic activity to "mature" before escaping into the surrounding control network.

Requirement of gap junctional intercellular communication for human villous trophoblast differentiation

During pregnancy, the villous trophoblast develops from the fusion of cytotrophoblastic cells (CT) into a syncytiotrophoblast (ST), supporting the main physiological functions of the human placenta. Connexin43 (Cx43) is demonstrated in situ and in vitro in the villous trophoblast between CT and between CT and ST. Moreover, the presence of a gap junctional intercellular communication (GJIC) during in vitro trophoblast differentiation was previously demonstrated. Because the exchange of molecules through gap junctions is considered to play a major role in the control of cell and tissue differentiation, we studied the effects of a gap junctional uncoupler, heptanol, on morphological and functional trophoblast differentiation and on GJIC measured by the fluorescence recovery after photobleaching method. We found that when the GJIC was interrupted, CT still aggregated but fused poorly. This morphological effect was associated with a significant decrease of trophoblastic-specific gene expression (beta human chorionic gonadotropin and human chorionic somatomammotropin). This blocking action was reversible as demonstrated by recovery of GJIC and trophoblast differentiation process after heptanol removal. Moreover, the inhibition of the trophoblast differentiation did not affect Cx43 transcript expression and Cx43 protein expression. These data suggest that the molecular exchanges through gap junctions preceding cellular fusion are essential for trophoblast differentiation generating the multifunctional syncytiotrophoblast.

The metabolic inhibitor antimycin A can disrupt cell-to-cell communication by an ATP- and Ca(2+)-independent mechanism

In cardiac myocytes of new-born rats, the degree of intercellular communication through gap junctional channels closely depends on the metabolic state of the cells. In contrast, in stably transfected HeLa cells expressing rat cardiac connexin43 (Cx43, the main channel-forming protein present in ventricular myocytes), a major part of junctional communication persisted in ATP-depleted conditions, in the presence of a metabolic inhibitor (KCN) or of a broad spectrum inhibitor of protein kinases (H7). However, another metabolic inhibitor, antimycin A, which like cyanide inhibits electron transfer in the respiratory chain, totally interrupted cell-to-cell communication between Cx43-HeLa cells, even in whole-cell conditions, when ATP (5 mM) was present. Antimycin A caused a modest increase in cytosolic calcium concentration; however, junctional uncoupling still occurred when this rise was prevented. Conditions of ischemic insult (e.g. ischemia or chemical hypoxia) frequently cause the activation of protein kinases, particularly of Src and MAP kinases, and such activations are known to markedly disrupt gap junctional communication. Antimycin-induced junctional uncoupling occurred even in the presence of inhibitors of these kinases. Antimycin A appears able to cause junctional uncoupling either through the ATP depletion it induces as a metabolic poison or via a direct action on gap junction constituents.

Fiber orientation and cell-cell coupling influence ventricular fibrillation dynamics

Cell Coupling Influences VF Dynamics.

INTRODUCTION

The structure of ventricular fibrillation (VF) is influenced by regional differences in action potential durations and perhaps restitution kinetics and fiber anisotropy. The spatial organization of VF was investigated by measuring the cross-correlation (CC) and mutual information (MI) of membrane potential (Vm) oscillations recorded from multiple sites.

METHODS AND RESULTS

Rabbit hearts (n = 6) were retrogradely perfused and stained with di-4-ANEPPS, and VF was elicited by burst pacing. Vm oscillations were recorded optically from multiple locations on the epicardium using a 16 x 16 photodiode array or a 72 x 78 CCD camera. The spatial organization of VF was investigated by calculating the maximum CC (CCmax) and MI (MImax) that can be obtained between any two sites. CCmax and MImax were extended to all pixels and served as indices of the similarities between Vm transients at a reference pixel and all other pixels on the map. We found that maps of CCmax and MImax did not contain discrete regions with high CC or MI. However, CCmax and MImax decreased monotonically with increasing distance between any arbitrarily chosen reference pixel and all other pixels. In VF, maps of CCmax and MImax revealed elliptical gradients of CC and MI that were closely aligned with fiber orientation, with major axis at 127 degrees +/- 8 degrees on the left ventricles.

CONCLUSION

CC and MI analysis in fibrillation provides new evidence that anisotropy of fiber orientation and cell-cell coupling have a direct influence on VF dynamics.

Regional gap junction inhibition increases defibrillation thresholds

It is clear that ischemia inhibits successful defibrillation by altering regional electro-physiology. However, the exact mechanisms are unclear. This study investigated whether regional gap junction inhibition increases biphasic shock defibrillation thresholds (DFT). Sixteen swine were instrumented with a mid-left anterior descending (LAD) perfusion catheter for regional infusion of 0.5 mM/h heptanol (n = 8) or saline (n = 8). DFT values and effective refractory periods (ERP) at five myocardial sites were determined. Regional conduction velocity (CV) was determined in an LAD drug-perfused and nondrug-perfused region in an additional seven swine. Regional heptanol infusion increased 50% DFT values by 33% (P = 0.01) and slowed CV by 42-59% (P < 0.01) but did not affect ERP. Regional heptanol also increased CV dispersion by approximately 270% (P < 0.05) but did not change ERP dispersion. Regional placebo did not alter any of these parameters. Furthermore, regional heptanol infusion induced spontaneous ventricular fibrillation in eight of eight animals. Increasing spatial conduction velocity dispersion by impairing regional gap junction conductance increased DFT values. Dispersion in conduction velocity slowing during regional ischemia may be an important determinant of defibrillation efficacy.

In situ Ca2+ imaging of odor responses in a coronal olfactory epithelium slice

An in situ Ca2+ -imaging technique was adopted to monitor odorant responses of more than several hundreds of neurons simultaneously in an intact coronal slice of the mouse olfactory epithelium. The sensitivity and resolution of the slice Ca2+ -imaging were high enough to distinguish between olfactory receptor neurons with threshold concentrations in a one-order difference for a particular odorant at the single-cell level. Increasing odorant concentrations resulted in increases in the numbers of odorant-responsive neurons, which were visualized in situ in the coronal slice. The methodology established in this study is a powerful tool to visualize spatial distributions of odorant responsive neurons at a cellular resolution, and to construct odor maps in a coronal view of the olfactory epithelium.

Increased connexin43-mediated intercellular communication in a rat model of bladder overactivity in vivo

Bladder overactivity associated with outflow obstruction is a common human condition recapitulated in the female rat by narrowing the diameter of the urethra. The goal of these studies was to evaluate the role of intercellular communication through connexin43 (Cx43)-derived gap junction channels to bladder overactivity following partial urethral outflow obstruction of 3-day to 6-wk duration. Cx43 mRNA and protein expression were barely detectable by Northern or Western blots, respectively, in the detrusor layer of normal bladders, but bands were found with both techniques after 6 wk of obstruction. Linear regression analysis of the RT-PCR data revealed a statistically significant positive correlation between the duration of obstruction (again, ranging from 3-day to 6-wk duration) and Cx43 mRNA transcript levels, such that after 6 wk of obstruction, Cx43 transcript levels were approximately 15-fold greater than initial control values. When taking into account the approximately fivefold increase in bladder weight over this same time frame, the absolute amount of Cx43 mRNA in the bladder apparently increased by approximately 75-fold. In that regard, as anticipated, and consistent with previous observations, 6 wk of obstruction was also associated with a significant increase in spontaneous bladder contractions between micturitions. The amplitude of these contractions was significantly reduced by heptanol given intravesically. Furthermore, carbachol-precontracted bladder strips from obstructed animals were more sensitive to heptanol-induced relaxation (100 microM) than their unobstructed counterparts (n = 6; P < 0.01). When bladder strips were equivalently precontracted via electrical field stimulation (EFS; 20 Hz), similar heptanol-induced relaxation responses were observed. However, the tetrodotoxin-resistant portion of the EFS-induced contraction was greater in the obstructed than in the unobstructed animals, and this portion of the contractile response was more sensitive to heptanol-induced relaxation in obstructed than unobstructed bladders (n = 7; P < 0.01). Taken together, these observations indicate that partial outlet obstruction produces an overactive bladder that may be more dependent on intercellular communication through gap junctions for modulation of contractile responses than its normal counterpart.

Functional hemichannels in astrocytes: a novel mechanism of glutamate release

Little is known about the expression and possible functions of unopposed gap junction hemichannels in the brain. Emerging evidence suggests that gap junction hemichannels can act as stand-alone functional channels in astrocytes. With immunocytochemistry, dye uptake, and HPLC measurements, we show that astrocytes in vitro express functional hemichannels that can mediate robust efflux of glutamate and aspartate. Functional hemichannels were confirmed by passage of extracellular lucifer yellow (LY) into astrocytes in nominal divalent cation-free solution (DCFS) and the ability to block this passage with gap junction blocking agents. Glutamate/aspartate release (or LY loading) in DCFS was blocked by multivalent cations (Ca2+, Ba2+, Sr2+, Mg2+, and La3+) and by gap junction blocking agents (carbenoxolone, octanol, heptanol, flufenamic acid, and 18alpha-glycyrrhetinic acid) with affinities close to those reported for blockade of gap junction intercellular communication. Glutamate efflux via hemichannels was also accompanied by greatly reduced glutamate uptake. Glutamate release in DCFS, however, was not significantly mediated by reversal of the glutamate transporter: release did not saturate and was not blocked by glutamate transporter blockers. Control experiments in DCFS precluded glutamate release by volume-sensitive anion channels, P2X7 purinergic receptor pores, or general purinergic receptor activation. Blocking intracellular Ca2+ mobilization by BAPTA-AM or thapsigargin did not inhibit glutamate release in DCFS. Divalent cation removal also induced glutamate release from intact CNS white matter (acutely isolated optic nerve) that was blocked by carbenoxolone, suggesting the existence of functional hemichannels in situ. Our results indicated that astrocyte hemichannels could influence CNS levels of extracellular glutamate with implications for normal and pathological brain function.

Relationship between molecular structure, concentration and odor qualities of oxygenated aliphatic molecules

Increasing the concentration of an odorant increases the number of receptor cells and glomeruli in the olfactory bulb that are stimulated, and it is commonly acknowledged that these represent increased numbers of receptor types. Currently, it is not known whether a receptor type is associated with a unique quality and a unique molecular feature of an odorant, or its activation is used by the brain in a combinatorial manner with other activated receptor types to produce a characteristic quality. The present study investigated the proposal that a molecular feature common to several aliphatic odorants and known to be the key feature required to stimulate the same mitral cells in the olfactory bulb results in a quality that is common to the odorants. Since the common structural feature may activate a specific receptor type possibly at a similar concentration, the qualities of the odorants were determined at seven concentrations where the lowest and highest concentrations were the detection threshold (DT) and 729DT of each subject. A list of 146 descriptors was used by 15 subjects to describe the qualities of each odorant at each concentration. The results indicate that each of the five odorants was characterized by different qualities and the qualities of four of the odorants changed with changes in concentration. Importantly, no quality common to each of the odorants that had the same molecular feature could be identified and it is proposed that identification of the odorants occurs via a combinatorial mechanism involving several types of receptors.