An actin filament population defined by the tropomyosin Tpm3.1 regulates glucose uptake

Actin has an ill-defined role in the trafficking of GLUT4 glucose transporter vesicles to the plasma membrane (PM). We have identified novel actin filaments defined by the tropomyosin Tpm3.1 at glucose uptake sites in white adipose tissue (WAT) and skeletal muscle. In Tpm 3.1-overexpressing mice, insulin-stimulated glucose uptake was increased; while Tpm3.1-null mice they were more sensitive to the impact of high-fat diet on glucose uptake. Inhibition of Tpm3.1 function in 3T3-L1 adipocytes abrogates insulin-stimulated GLUT4 translocation and glucose uptake. In WAT, the amount of filamentous actin is determined by Tpm3.1 levels and is paralleled by changes in exocyst component (sec8) and Myo1c levels. In adipocytes, Tpm3.1 localizes with MyoIIA, but not Myo1c, and it inhibits Myo1c binding to actin. We propose that Tpm3.1 determines the amount of cortical actin that can engage MyoIIA and generate contractile force, and in parallel limits the interaction of Myo1c with actin filaments. The balance between these actin filament populations may determine the efficiency of movement and/or fusion of GLUT4 vesicles with the PM.

Regulation and control of myosin-I by the motor and light chain-binding domains

Members of the myosin-I family of molecular motors are expressed in many eukaryotes, where they are involved in a multitude of critical processes. Humans express eight distinct members of the myosin-I family, making it the second largest family of myosins expressed in humans. Despite the high degree of sequence conservation in the motor and light chain-binding domains (LCBDs) of these myosins, recent studies have revealed surprising diversity of function and regulation arising from isoform-specific differences in these domains. Here we review the regulation of myosin-I function and localization by the motor and LCBDs.

Calcium regulation of myosin-I tension sensing

Myo1b is a myosin that is exquisitely sensitive to tension. Its actin-attachment lifetime increases > 50-fold when its working stroke is opposed by 1 pN of force. The long attachment lifetime of myo1b under load raises the question: how are actin attachments that last >50 s in the presence of force regulated? Like most myosins, forces are transmitted to the myo1b motor through a light-chain binding domain that is structurally stabilized by calmodulin, a calcium-binding protein. Thus, we examined the effect of calcium on myo1b motility using ensemble and single-molecule techniques. Calcium accelerates key biochemical transitions on the ATPase pathway, decreases the working-stroke displacement, and greatly reduces the ability of myo1b to sense tension. Thus, calcium provides an effective mechanism for inhibiting motility and terminating long-duration attachments.

Kinetic schemes for post-synchronized single molecule dynamics

Recordings from single molecule experiments can be aggregated to determine average kinetic properties of the system under observation. The kinetics after a synchronized reaction step can be interpreted using all of the standard tools developed for ensemble perturbation experiments. The kinetics leading up to a synchronized event, determined by the lifetimes of the preceding states; however, are not as obvious if the reaction has reversible steps or branches. Here we describe a general procedure for dealing with these situations.

A hearing loss-associated myo1c mutation (R156W) decreases the myosin duty ratio and force sensitivity

myo1c is a member of the myosin superfamily that has been proposed to function as the adaptation motor in vestibular and auditory hair cells. A recent study identified a myo1c point mutation (R156W) in a person with bilateral sensorineural hearing loss. This mutated residue is located at the start of the highly conserved switch 1 region, which is a crucial element for the binding of nucleotide. We characterized the key steps on the ATPase pathway at 37 °C using recombinant wild-type (myo1c(3IQ)) and mutant myo1c (R156W-myo1c(3IQ)) constructs that consist of the motor domain and three IQ motifs. The R156W mutation only moderately affects the rates of ATP binding, ATP-induced actomyosin dissociation, and ADP release. The actin-activated ATPase rate of the mutant is inhibited >4-fold, which is likely due to a decrease in the rate of phosphate release. The rate of actin gliding, as measured by the in vitro motility assay, is unaffected by the mutation at high myosin surface densities, but the rate of actin gliding is substantially reduced at low surface densities of R156W-myo1c(3IQ). We used a frictional loading assay to measure the affect of resisting forces on the rate of actin gliding and found that R156W-myo1c(3IQ) is less force-sensitive than myo1c(3IQ). Taken together, these results indicate that myo1c with the R156W mutation has a lower duty ratio than the wild-type protein and motile properties that are less sensitive to resisting forces.

Cardiomyopathy-linked myosin regulatory light chain mutations disrupt myosin strain-dependent biochemistry

Familial hypertrophic cardiomyopathy (FHC) is caused by mutations in sarcomeric proteins including the myosin regulatory light chain (RLC). Two such FHC mutations, R58Q and N47K, located near the cationic binding site of the RLC, have been identified from population studies. To examine the molecular basis for the observed phenotypes, we exchanged endogenous RLC from native porcine cardiac myosin with recombinant human ventricular wild type (WT) or FHC mutant RLC and examined the ability of the reconstituted myosin to propel actin filament sliding using the in vitro motility assay. We find that, whereas the mutant myosins are indistinguishable from the controls (WT or native myosin) under unloaded conditions, both R58Q- and N47K-exchanged myosins show reductions in force and power output compared with WT or native myosin. We also show that the changes in loaded kinetics are a result of mutation-induced loss of myosin strain sensitivity of ADP affinity. We propose that the R58Q and N47K mutations alter the mechanical properties of the myosin neck region, leading to altered load-dependent kinetics that may explain the observed mutant-induced FHC phenotypes.

The molecular basis of frictional loads in the in vitro motility assay with applications to the study of the loaded mechanochemistry of molecular motors

Molecular motors convert chemical energy into mechanical movement, generating forces necessary to accomplish an array of cellular functions. Since molecular motors generate force, they typically work under loaded conditions where the motor mechanochemistry is altered by the presence of a load. Several biophysical techniques have been developed to study the loaded behavior and force generating capabilities of molecular motors yet most of these techniques require specialized equipment. The frictional loading assay is a modification to the in vitro motility assay that can be performed on a standard epifluorescence microscope, permitting the high-throughput measurement of the loaded mechanochemistry of molecular motors. Here, we describe a model for the molecular basis of the frictional loading assay by modeling the load as a series of either elastic or viscoelastic elements. The model, which calculates the frictional loads imposed by different binding proteins, permits the measurement of isotonic kinetics, force-velocity relationships, and power curves in the motility assay. We show computationally and experimentally that the frictional load imposed by alpha-actinin, the most widely employed actin binding protein in frictional loading experiments, behaves as a viscoelastic rather than purely elastic load. As a test of the model, we examined the frictional loading behavior of rabbit skeletal muscle myosin under normal and fatigue-like conditions using alpha-actinin as a load. We found that, consistent with fiber studies, fatigue-like conditions cause reductions in myosin isometric force, unloaded sliding velocity, maximal power output, and shift the load at which peak power output occurs.

The direct molecular effects of fatigue and myosin regulatory light chain phosphorylation on the actomyosin contractile apparatus

Skeletal muscle, during periods of exertion, experiences several different fatigue-based changes in contractility, including reductions in force, velocity, power output, and energy usage. The fatigue-induced changes in contractility stem from many different factors, including alterations in the levels of metabolites, oxidative damage, and phosphorylation of the myosin regulatory light chain (RLC). Here, we measured the direct molecular effects of fatigue-like conditions on actomyosin's unloaded sliding velocity using the in vitro motility assay. We examined how changes in ATP, ADP, P(i), and pH affect the ability of the myosin to translocate actin and whether the effects of each individual molecular species are additive. We found that the primary causes of the reduction in unloaded sliding velocity are increased [ADP] and lowered pH and that the combined effects of the molecular species are nonadditive. Furthermore, since an increase in RLC phosphorylation is often associated with fatigue, we examined the differential effects of myosin RLC phosphorylation and fatigue on actin filament velocity. We found that phosphorylation of the RLC causes a 22% depression in sliding velocity. On the other hand, RLC phosphorylation ameliorates the slowing of velocity under fatigue-like conditions. We also found that phosphorylation of the myosin RLC increases actomyosin affinity for ADP, suggesting a kinetic role for RLC phosphorylation. Furthermore, we showed that ADP binding to skeletal muscle is load dependent, consistent with the existence of a load-dependent isomerization of the ADP bound state.

The molecular effects of skeletal muscle myosin regulatory light chain phosphorylation

Phosphorylation of the myosin regulatory light chain (RLC) in skeletal muscle has been proposed to act as a molecular memory of recent activation by increasing the rate of force development, ATPase activity, and isometric force at submaximal activation in fibers. It has been proposed that these effects stem from phosphorylation-induced movement of myosin heads away from the thick filament backbone. In this study, we examined the molecular effects of skeletal muscle myosin RLC phosphorylation using in vitro motility assays. We showed that, independently of the thick filament backbone, the velocity of skeletal muscle myosin is decreased upon phosphorylation due to an increase in the myosin duty cycle. Furthermore, we did not observe a phosphorylation-dependent shift in calcium sensitivity in the absence of the myosin thick filament. These data suggest that phosphorylation-induced movement of myosin heads away from the thick filament backbone explains only part of the observed phosphorylation-induced changes in myosin mechanics. Last, we showed that the duty cycle of skeletal muscle myosin is strain dependent, consistent with the notion that strain slows the rate of ADP release in striated muscle.

Regulatory light chain mutations associated with cardiomyopathy affect myosin mechanics and kinetics

The myosin regulatory light chain (RLC) wraps around the alpha-helical neck region of myosin. This neck region has been proposed to act as a lever arm, amplifying small conformational changes in the myosin head to generate motion. The RLC serves an important structural role, supporting the myosin neck region and a modulatory role, tuning the kinetics of the actin myosin interaction. Given the importance of the RLC, it is not surprising that mutations of the RLC can lead to familial hypertrophic cardiomyopathy (FHC), the leading cause of sudden cardiac death in people under 30. Population studies identified two FHC mutations located near the cationic binding site of the RLC, R58Q and N47K. Although these mutations are close in sequence, they differ in clinical presentation and prognosis, with R58Q showing a more severe phenotype. We examined the molecular based changes in myosin that are responsible for the disease phenotype by purifying myosin from transgenic mouse hearts expressing mutant myosins and examining actin filament sliding using the in vitro motility assay. We found that both R58Q and N47K show reductions in force compared to the wild type that could result in compensatory hypertrophy. Furthermore, we observed a higher ATPase rate and an increased activation at submaximal calcium levels for the R58Q myosin that could lead to decreased efficiency and incomplete cardiac relaxation, potentially explaining the more severe phenotype for the R58Q mutation.

Modulation of actin mechanics by caldesmon and tropomyosin

The ability of cells to sense and respond to physiological forces relies on the actin cytoskeleton, a dynamic structure that can directly convert forces into biochemical signals. Because of the association of muscle actin-binding proteins (ABPs) may affect F-actin and hence cytoskeleton mechanics, we investigated the effects of several ABPs on the mechanical properties of the actin filaments. The structural interactions between ABPs and helical actin filaments can vary between interstrand interactions that bridge azimuthally adjacent actin monomers between filament strands (i.e. by molecular stapling as proposed for caldesmon) or, intrastrand interactions that reinforce axially adjacent actin monomers along strands (i.e. as in the interaction of tropomyosin with actin). Here, we analyzed thermally driven fluctuations in actin's shape to measure the flexural rigidity of actin filaments with different ABPs bound. We show that the binding of phalloidin increases the persistence length of actin by 1.9-fold. Similarly, the intrastrand reinforcement by smooth and skeletal muscle tropomyosins increases the persistence length 1.5- and 2- fold respectively. We also show that the interstrand crosslinking by the C-terminal actin-binding fragment of caldesmon, H32K, increases persistence length by 1.6-fold. While still remaining bound to actin, phosphorylation of H32K by ERK abolishes the molecular staple (Foster et al. 2004. J Biol Chem 279;53387-53394) and reduces filament rigidity to that of actin with no ABPs bound. Lastly, we show that the effect of binding both smooth muscle tropomyosin and H32K is not additive. The combination of structural and mechanical studies on ABP-actin interactions will help provide information about the biophysical mechanism of force transduction in cells.

Hydrogen sulfide is synthesized in the gills of the clam Mercenaria mercenaria and acts seasonally to modulate branchial muscle contraction

Previously we showed that when the gill muscles of the venerid clam Mercenaria mercenaria are stimulated to contract by 5-hydroxytryptamine (5HT), the contraction is about doubled when another identical dose of 5HT is applied after washout. Furthermore, this "endogenous potentiation" is mimicked by nitric oxide (NO), which is synthesized in the gill. We now report that the isolated gills also synthesize H2S; the basal rate of synthesis was 0.70 micromol.g(-1).h(-1) (se = 0.14; n = 24), but in the presence of 5HT (10(-2) M), the rate increased markedly to 35.82 micromol.g(-1).h(-1) (se = 4.93; n = 4). In addition, dithiothreitol (DTT; 2.2 mM) increased the rate of synthesis significantly to 4.9 micromol.g(-1).h(-1) (se = 0.8; n = 8). Stimulation of H2S synthesis by 5HT (5 x 10(-3) M) was seasonal; that is, the rates measured monthly from December through June are significantly lower than those measured from July through November. We also found that if isolated gills were pretreated with the H2S donor, sodium hydrosulfide (NaHS), their contractions in response to 5HT were potentiated. The threshold of the potentiation was 10(-8) M NaHS, and the largest effect was at 10(-6) M. During August, however, when endogenous and NO-induced potentiations are both absent, 10(-6) M NaHS was also ineffective. Like the effect of NO, that of NaHS (10(-6) M) was blocked by oxadiasoloquinoxalin (ODQ; 5 x 10(-5) M), an inhibitor of soluble guanylate cyclase (sGC). Moreover, Rp-8-CPT-cGMPS (10(-5) M), which inhibits protein kinase-G, also blocked the effect of NaHS (10(-6) M). When isolated gills were treated with 2.2 mM DTT, the endogenous potentiation of a second 5HT-induced contraction more than doubled in comparison to untreated controls. In conclusion, H2S is synthesized in the gill and, along with NO, is a seasonal, endogenous modulator of branchial muscle contraction; its action may be mediated through a sGC/cGMP signaling cascade.

Nitric oxide mediates seasonal muscle potentiation in clam gills

The physiology and timing of gill muscle potentiation were explored in the clam Mercenaria mercenaria. When isolated demibranchs were exposed twice (with an intervening wash) to the same concentration of 5-hydroxytryptamine, the second contraction was larger than the first. This potentiation was seasonal: it was present from November through June, and absent from July through October. Potentiation was not affected by the geographic origin of the clams, nor by their acclimation temperature. Potentiation was inhibited by the nitric oxide synthase (NOS) inhibitor L-NAME and mimicked by the nitric oxide (NO) donor DEANO. During the season of potentiation, immunoreactive NOS appeared in the gill muscles and the gill filament epithelium, but during the off-season, the enzyme occurred at the base of the gill filaments. Potentiation was inhibited by ODQ, which inhibits soluble guanylate cyclase (sGC), and it was mimicked by dibutyryl-cGMP, an analog of cyclic GMP (cGMP). Moreover, potentiation was inhibited by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMPS. During the season of potentiation, immunoreactive sGC was concentrated in the gill muscles and the gill filament epithelium; but during the off-season, immunoreactive sGC was found in the gill filament epithelium. These data suggest that the potentiation of gill muscle is mediated by a NO/cGMP/PKG signaling pathway.

Branchial musculature of a venerid clam: pharmacology, distribution, and innervation

This study was meant to analyze the neural control of the branchial muscles of the clam Mercenaria mercenaria. Gills isolated from the animal contract in response to 5-hydroxytryptamine (5HT), dopamine (DA), and acetylcholine (ACh); but the ACh contraction occurred only if the gills had been pretreated with the cholinesterase inhibitor eserine. The 5HT antagonists cyproheptadine and mianserin blocked the contractile effects of all of the agonists. However, gills exposed to the 5HT antagonists and eserine relaxed in response to ACh. The DA antagonist SCH-83566 inhibited the effects of DA, but had no effect on contractions induced by 5HT and ACh. The ACh antagonist hexamethonium inhibited both the excitatory and inhibitory effects of ACh, but had no effect on contractions induced by 5HT and DA. 5HT and DA in gill tissue were visualized by using immunohistochemistry. Within each gill filament are dorsoventral neurons running adjacent to the epithelium and containing immunoreactive 5HT and DA. A complex network of 5HT-positive fibers is associated with the septa, blood vessels, and muscles, whereas DA-positive fibers are restricted to the septa. We propose that 5HT is the excitatory transmitter to the gill muscles, and that DA and ACh exert their excitatory effects by stimulating 5HT motor nerves. ACh may also be an inhibitory transmitter of the muscles.

Organ preservation therapy using induction plus concurrent chemoradiation for advanced resectable oropharyngeal carcinoma: a University of Pennsylvania Phase II Trial

PURPOSE

To determine the efficacy, feasibility, and toxicity of a new regimen for locally advanced oropharyngeal carcinoma.

PATIENTS AND METHODS

Patients had technically resectable stage III/IV squamous cell carcinoma of the oropharynx, exclusive of T1-2N1. Induction chemotherapy consisted of carboplatin (area under the curve formula equal to 6) and paclitaxel 200 mg/m(2) for two cycles, followed by re-evaluation. Patients with major response continued to definitive radiotherapy (70 Gy over 7 weeks) plus concurrent once-weekly paclitaxel (30 mg/m(2)/wk). Patients with advanced neck disease also underwent post-radiation therapy neck dissection and two more chemotherapy cycles.

RESULTS

Fifty-three patients were enrolled. Median follow-up was 31 months (minimum follow-up for survivors was 18 months). The major response rate to induction chemotherapy was 89%; 90% of patients had a complete response after concurrent chemoradiation. Actuarial survival at 3 years was 70%, and 3-year event-free survival was 59%. The 3-year actuarial locoregional control was 82% and the 3-year actuarial rate of distant metastases was 19%. Organ preservation was achieved in 77% of all patients. One patient (2%) died during therapy. Late grade 3 toxicity occurred in 24% of patients, consisting mainly of chronic dysphagia/aspiration and/or radiation soft tissue ulceration. The treatment-related mortality rate was 4% (two patients died from respiratory failure).

CONCLUSION

Response to induction chemotherapy as studied in this trial was not useful as a predictive marker for ultimate outcome or organ conservation. Overall, however, this regimen offers good disease control and survival for patients with locally advanced oropharyngeal carcinoma, comparable with other concurrent chemoradiation programs. Further study of similar protocols is indicated.

Visceral regeneration in holothurians

Holothurians, or sea cucumbers, exhibit two processes that have intrigued biologists for decades: autotomy and regeneration. Autotomy includes the loss of body parts by evisceration or fission, and regeneration is the extraordinary process by which the lost organs are replaced. In this article, we review the literature on evisceration, transection, and visceral regeneration in holothurians and compare these processes in different orders and lower taxa. Focusing mainly on the digestive tube, we analyze regeneration from a cellular perspective, considering especially the origin, migration, and proliferation of the cellular components of the regenerated organ. The data highlight the most interesting aspects of holothurian regeneration and indicate those critical problems requiring new information and new approaches.

Pentobarbital for severe gamma-butyrolactone withdrawal

STUDY OBJECTIVE

Gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) have become popular drugs of abuse. Acute overdose with either agent results in a well-recognized syndrome of central nervous system and respiratory depression. Recently, a withdrawal syndrome has been described for GHB. We report a severe form of GBL withdrawal, characterized by delirium, psychosis, autonomic instability, and resistance to benzodiazepine therapy.

METHODS

We performed a chart review of consecutive admissions for GBL withdrawal in a regional toxicology treatment center.

RESULTS

During a 6-month period, 5 patients presented with severe withdrawal attributed to abrupt GBL discontinuation. Patients manifested tachycardia, hypertension, paranoid delusions, hallucinations, and rapid fluctuations in sensorium. Test results for ethanol and routine drugs of abuse were negative. Initial treatment with high doses of lorazepam proved ineffective. Pentobarbital was then administered, resulting in excellent control of behavioral, autonomic, and psychiatric symptoms and in rapid reduction or avoidance of benzodiazepines. Median hospital stay was 5 days. No patient had respiratory depression or required mechanical ventilation. Patients were discharged on tapering doses of benzodiazepines or pentobarbital and were free of psychotic symptoms at follow-up.

CONCLUSION

GBL discontinuation can result in severe withdrawal, necessitating ICU admission. Pentobarbital may be more effective than benzodiazepines at controlling delirium in patients with abnormal vital signs, paranoid delusions, and hallucinations as a result of GBL withdrawal.

Pilot study of organ preservation multimodality therapy for locally advanced resectable oropharyngeal carcinoma

The purpose of this study was to determine the early efficacy and toxicity of a new multimodality organ-preservation regimen for locally advanced, resectable oropharyngeal squamous cell carcinoma (SCC). Patients with T3-4N0-3M0 or T2N2-3M0 oropharyngeal SCC were eligible for this Phase II study. Patients needed the physiologic reserve for surgery and technically resectable tumors. Induction carboplatin (area under the curve = 6) and paclitaxel (200 mg/m2) x 2 cycles (q21 days) were given. Objective responders received definitive radiotherapy (XRT), 70 Gy/7 weeks with concurrent weekly paclitaxel. Initially, the dose of paclitaxel was 50 mg/m2/week; because of mucosal toxicity it was reduced to 30 mg/m2/week. Patients with N2-3 disease received post-XRT neck dissection and 2 more cycles of "adjuvant" chemotherapy. In the first 22 patients, the neutropenic fever rate was 27%. Although there has been no grade IV-V toxicity from induction therapy, grade II-III toxicity resulted in an unacceptable delay in starting XRT in 14% of patients. The response rate to induction chemotherapy was 91%. Grade III mucositis occurred in all patients during concurrent chemoradiotherapy. One patient died of pneumonia during concurrent chemoradiotherapy after receiving 26 Gy and 3 doses of paclitaxel 50 mg/m2. No dose-limiting toxicity occurred in 15 patients treated with concurrent paclitaxel 30 mg/m2/week. Actuarial overall survival at 18 months is 82%; local-regional control is 86%. To date, distant metastases have not developed in any patients. This regimen has intense but acceptable acute toxicity. The maximum tolerated dosage of weekly paclitaxel during standard continuous-course XRT is confirmed to be 30 mg/m2/week. The treatment efficacy of this regimen (response rate and short-term local-regional and distant control) is encouraging. Accrual continues to obtain long-term toxicity, efficacy, and quality-of-life data.

An endogenous SCP-related peptide modulates ciliary beating in the gills of a venerid clam, Mercenaria mercenaria

The activities of both the lateral and frontal cilia of Mercenaria mercenaria were unaffected, either by the two endogenous SCP-related peptides AMSFYFPRMamide and YFAFPRQamide, or by FMRFamide (all at 10(-6) M). Dopamine (DA) inhibited the lateral cilia; the mean EC50 was 2 x 10(-6) M. The peptide YFAFPRQamide--but neither AMSFYFPRMamide nor FMRFamide--antagonized the inhibition induced by DA; this effect was dependent on both time and dose. At a DA concentration of 5 x 10(-7) M, the effect of YFAFPRQamide appeared within 20 min and became maximal within 40-60 min; the mean EC50 at these times was 4.7 x 10(-11) M. If the concentration of DA was increased to 10(-6) M, the maximal effect of the peptide was delayed to 50 min, and the mean EC50 increased to 1.1 x 10(-7) M. Particle transport by the frontal cilia was inhibited by 5-hydroxytryptamine (5HT); the mean EC50 was 5.7 x 10(-7) M. Again, only YFAFPRQamide had an antagonistic effect on the 5HT-induced inhibition. At a 5HT concentration of 10(-6) M, the effects of YFAFPRQamide did not appear until 45 min; the mean EC50 was 10(-6) M. When radioimmunoassayed with an SCP antiserum, the elution profile of a gill extract overlapped those of the SCP-related peptides that had previously been identified in extracts of whole animals. These data suggest that all three SCP analogs occur in the gill. Immunohistochemistry of the gill, carried out with a monoclonal antibody raised to SCPB, stained many varicose neuronal fibers. Most of these were associated with the gill musculature, but a sparse innervation of the filaments underlying the cilia was also observed. Some fluorescent nerve cell bodies were also seen in the gill tissue. Our results are consistent with the hypothesis that YFAFPRQamide modulates branchial activities--muscular as well as ciliary--that are associated with feeding.

Surgical repair of an atrial septal defect in a juvenile Sumatran orangutan (Pongo pygmaeus sumatraensis)

A systolic heart murmur was auscultated in a 2-yr-old female Sumatran orangutan (Pongo pygmaeus sumatraensis) with a slower than expected growth rate. Cardiac ultrasound revealed an 11-mm atrial septal defect. Cardiac catheterization confirmed the diagnosis. Surgical repair was performed during cardiopulmonary bypass using a pericardial patch. The bypass pump was primed with human albumin and donor orangutan whole blood of a compatible type. Hematuria occurred shortly after the initiation of cardiopulmonary bypass. Successful repair was immediately confirmed with transesophageal ultrasonography. The animal was extubated shortly after returning to spontaneous ventilation but had to be reintubated 4 hr later due to tachypnea and decreased SpO2. Additional extubation attempts failed, necessitating continuous positive pressure ventilation, monitoring, and intensive care environment. Thoracic radiographs suggested adult respiratory distress syndrome. The animal required 14 days of intensive care before extubation of the trachea was successful. After 4 wk of isolation, the orangutan was successfully reintroduced to its family group.

Relationships between ligand affinities for the cerebellar cannabinoid receptor CB1 and the induction of GDP/GTP exchange

The hypothesis of these studies is that ligand efficacy at the neuronal CB1 receptor is dependent on the ratio of ligand affinities for the active and inactive states of the receptor. Agonist efficacy was determined in rat cerebellar membranes using agonist-induced guanosine 5'-O-(3-[35S]thiotriphosphate) binding; efficacy was variable among the CB1 agonists examined. Ligand affinities for the active and inactive state of the CB1 receptor were determined by competition with [3H]CP55940 and [3H]SR141716A in the presence of 5'-guanylylimidodiphosphate, respectively. All of the agonists investigated had a higher affinity for the active state than the inactive state. The fraction of CB1 receptors in the active state at a maximally effective concentration was calculated for each agonist and was found to correlate significantly with agonist efficacy. These studies demonstrate that the CB1 receptor of the cerebellum can assume an active conformation in the absence of agonist and that the variability in efficacy among CB1 receptor agonists can be explained by the relative affinities of these ligands for the CB1 receptor in the active and inactive states.

Synthesis and characterization of potent and selective agonists of the neuronal cannabinoid receptor (CB1)

Two subtypes of the cannabinoid receptor (CB1 and CB2) are expressed in mammalian tissues. Although selective antagonists are available for each of the subtypes, most of the available cannabinoid agonists bind to both CB1 and CB2 with similar affinities. We have synthesized two analogs of N-arachidonylethanolamine (AEA), arachidonylcyclopropylamide (ACPA) and arachidonyl-2-chloroethylamide (ACEA), that bind to the CB1 receptor with very high affinity (KI values of 2.2 +/- 0.4 nM and 1.4 +/- 0.3 nM, respectively) and to the CB2 receptor with low affinity (KI values of 0.7 +/- 0.01 microM and 3.1 +/- 1.0 microM, respectively). Both ACPA and ACEA have the characteristics of agonists at the CB1 receptor; both inhibit forskolin-induced accumulation of cAMP in Chinese hamster ovary cells expressing the human CB1 receptor, and both analogs increase the binding of [35S]GTPgammaS to cerebellar membranes and inhibit electrically evoked contractions of the mouse vas deferens. ACPA and ACEA produce hypothermia in mice, and this effect is inhibited by coadministration of the CB1 receptor antagonist SR141716A. Therefore, ACPA and ACEA are high-affinity agonists of the CB1 receptor but do not bind the CB2 receptor, suggesting that structural analogs of AEA can be designed with considerable selectivity for the CB1 receptor over the CB2 receptor.

Osmoregulation and FMRFamide-related peptides in the salt marsh snail Melampus bidentatus (Say) (Mollusca: Pulmonata)

The pulmonate snail Melampus bidentatus occupies the high intertidal zone of salt marshes in a nearly terrestrial environment. The hemolymph osmolarity of the snails collected in the field paralleled that of the adjacent water and was affected by the tides and precipitation. The snails initially gained or lost weight when submerged in hypo- or hyperosmotic media, respectively, but returned to their original weight after 24 h. The content of their immunoreactive (IR)-FMRFamide-Related Peptides (FaRPs) was measured in various tissues by radioimmunoassay, and IR-FaRPs were found in every tissue analyzed. The subesophageal part of the central nervous system (CNS) contained more IR-FaRPs than the supraesophageal part, and the kidney and the tissues of the reproductive tract contained more than other peripheral tissues. The levels of IR-FaRPs in the CNS, kidney, and hemolymph were higher in snails that were immersed in higher concentrations of seawater. Many IR neurons are present in all ganglia of the CNS except the pleural ganglia, and IR neurites are extensively distributed within the CNS and its connective tissue sheath. The visceral nerve from the visceral ganglion is immunoreactive and could be seen to innervate the kidney, which contains IR-varicosities. An osmoregulatory role for the FaRPs is suggested.

Synthesis and characterization of diazomethylarachidonyl ketone: an irreversible inhibitor of N-arachidonylethanolamine amidohydrolase

N-Arachidonylethanolamine (AEA), a putative endogenous agonist of neuronal (CB1) cannabinoid receptors, is a substrate for N-arachidonylethanolamine amidohydrolase (AEA amidohydrolase), a serine amidase present in cell membranes. Following a strategy that has been used to develop inhibitors that covalently bind to the active site of serine peptidases, diazomethyl arachidonyl ketone (DAK) was synthesized and its effects on AEA amidohydrolase were determined. DAK inhibits the hydrolysis of AEA by rat brain membranes with an IC50 value of 0.5 microM. At low concentrations, DAK reduces the Vmax and increases the K(m) of the enzyme for its substrate AEA, which suggests that it is both a competitive and noncompetitive inhibitor. At higher concentrations, DAK inhibition is completely noncompetitive. DAK inhibition of membrane-associated AEA amidohydrolase is irreversible because hydrolytic activity is not restored with extensive washing or dialysis of the membranes. Furthermore, DAK inhibition is not reversible by anion exchange chromatography of the subsequently solubilized enzyme. In contrast, DAK inhibition of detergent-solubilized enzyme exhibits competitive kinetics and is reversible upon ion exchange chromatography. Exposure of C6 glioma cells to DAK results in concentration-related inhibition of AEA amidohydrolase activity in cellular membranes with an IC50 value of 0.3 microM. In summary, these studies demonstrate that DAK is an irreversible inhibitor of AEA amidohydrolase in its native membrane and provides a useful tool with which to study the role of AEA amidohydrolase in the termination of action of AEA.

FMRFamide-related peptides, partial serotonin depletion, and osmoregulation in Helisoma duryi (Mollusca: Pulmonata)

Serotonergic neurons were studied by specific histological methods, and neurons containing Phe-Met-Arg-Phe-NH2 (FMRFamide)-related heptapeptides were identified with an antiserum specific for these substances in the central nervous system of the freshwater snail Helisoma duryi. Serotonergic neurons and their axons are present in all of the ganglia (paired buccal, cerebral, pedal, pleural, parietal, and single visceral) and major nerves of the central nervous system. Large neurons containing FMRFamide-related peptide immunoreactivity are located in the left parietal and visceral ganglia, whereas a few small neurons are located in the cerebral and pedal ganglia. Both serotonergic and FMRFamide-related peptide-immunoreactive dendrites and varicosities were observed in the kidney. A second antiserum with high affinity for FMRFamide-related heptapeptides was used to measure the levels of the immunoreactive material in various tissues, and such material was found in every tissue analyzed. When snails were exposed to a medium isosmotic to their hemolymph, the levels of immunoreactive FMRFamide-related peptides increased in the hemolymph, central nervous system, mantle, and kidney. Injection of dihydroxytryptamine, which is known to deplete serotonin content in the snail, also reduced the levels of FMRFamide-related-immunoreactive material in the above tissues. Therefore, serotonin may influence the levels of FMRFamide-related peptides in tissues by regulating the rate of their synthesis, axonal transport, or release. Both serotonin and FMRFamide-related peptides could be involved in osmoregulation.

Pharmacology of the serotonergic inhibition of steroid-induced reinitiation of oocyte meiosis in the teleost Fundulus heteroclitus

Serotonin (5-HT) was found to inhibit steroid (17 alpha,20 beta-dihydroxy-4-pregnen-3-one; 17,20 beta P)-induced resumption of oocyte meiosis (oocyte maturation) in vitro in the teleost Fundulus heteroclitus. Serotonin inhibited both follicle-enclosed and denuded oocytes, which indicates the presence of oocyte-associated 5-HT sensitive sites. The response of oocytes to 5-HT was characterized pharmacologically, i.e., the capacity of serotonergic agonists and antagonists to mimic or block the 5-HT inhibition of the steroid-induced oocyte maturation was assessed by the changes in the percentage of oocyte germinal vesicle breakdown (GVBD). Dose-response curves for each compound were drawn and compared. The rank order of potency among the agonists was: 5-HT > 5-methoxytryptamine > tryptamine = 5,6-diHT = 5-carboxidotryptamine > 5,7-diHT = 5-methoxy-dimethyltryptamine > alpha-methyl-5HT > 2-methyl-5HT. Incubation of ovarian follicles with high doses of some antagonists (mianserin and metergoline) induced oocyte GVBD, although this effect was associated with high levels of oocyte atresia during GVBD or shortly after maturation. Consequently, doses of the antagonist too low to induce GVBD were tested for their ability to block the 5-HT inhibitory action; the rank order of potency was: MDL-72222 = metoclopramide > metergoline > propanolol > ketanserin. Dopamine, acetylcholine, epinephrine, and norepinephrine could also inhibit 17,20 beta P-induced GVBD, although at doses much higher than those of 5-HT; melatonin and histamine had no effect on oocyte maturation. These results suggest that specific receptors mediate the inhibitory action of 5-HT on the steroid-triggered meiosis resumption. The pharmacological profile of these 5-HT receptors is different from those of any known mammalian 5-HT receptor, although they showed some similarities to the 5-HT1A, 5-HT2, and 5-HT3 receptors, as well as to 5-HT receptors on oocytes of some bivalve molluscs.

Gastric outlet obstruction and epidermolysis bullosa

We describe a case of pyloric atresia coexisting with epidermolysis bullosa, almost certainly of the junctional type. The coexistence of pyloric atresia and junctional epidermolysis bullosa (PA-JEB syndrome) has been repeatedly observed. This syndrome has several clinical features that distinguish it from Herlitz junctional epidermolysis bullosa (JEB). These include a lack of prominent granulation tissue formation and increased frequencies of genitourinary tract involvement and ear anomalies. Aplasia cutis congenita is sometimes present; esophageal atresia is uncommonly present. In all 12 patients examined to date, normal basement membrane zone expression of laminin-5 biochemically distinguishes PA-JEB syndrome from Herlitz JEB. Mutations in the beta 4 integrin gene have been observed in one patient with PA-JEB syndrome. Thus there are both clinical and biochemical reasons to separate the PA-JEB syndrome from Herlitz JEB. This is the second known case of papillary hyperplasia of the amnion to be seen in any setting. The other was a case of JEB without pyloric atresia.

Effects of cardioactive peptides on myocardial cAMP levels in the snail Helix aspersa

Several cardioactive peptides from the pulmonate snail Helix aspersa were tested for their effects on myocardial cAMP levels, but only the family of small cardioactive peptides (SCPs) were clearly effective. SCP increased cAMP in a dose dependent manner; the time course was phasic. The structure-activity relations of this effect were examined with a set of 3 synthetic analogs having characteristics, at the carboxyterminal, of both the SCPs and FMRFamide-related peptides. The adenylate cyclase activator forskolin mimicked the mechanical effect of SCPs on the heartbeat. We conclude that the effect of SCPs on the Helix heart may be mediated by cAMP.

Protein phosphorylation in snail cardiocytes stimulated with molluscan peptide SCPb

Dissociated muscle cells prepared from hearts of the pulmonate snail Helix aspersa were used to study signal transduction induced by molluscan cardioactive peptides. The effects of SCPb on the cAMP levels of whole hearts and the cell preparation were compared. The cells responded to SCPb with a dose-dependent increase in cAMP that had the same structure-activity relations as seen in the intact tissue. SCPb increased the phosphorylation of a 53 kDa protein in a dose dependent manner; threshold was 10(-9) M. The SCPb-induced phosphorylation was mimicked by forskolin and 8-CPT-cAMP. FMRFamide stimulation had no effect on the phosphorylation of this protein.

Characterization of myomodulin-related peptides from the pulmonate snail Helix aspersa

Three myomodulin-related peptides--pQLSMLRLamide, PMSMLRLamide, and SLGMLRLamide--have been purified and sequenced from extracts of whole snails. The level of immunoreactive myomodulin was shown by HPLC and RIA to be widely distributed among 26 different snail tissues, with the highest levels (higher even than those in the central ganglia) occurring in certain male reproductive organs. Synthetic pQLSMLRLamide modified either the spontaneous rhythmic activity or the resting tone of several isolated muscular organs: the aorta, ventricle, upper gut, epiphallus, flagellum, and spermatheca; but the retractor muscles of the pharynx, penis, and tentacle were unaffected.

The peptide pQFYRFamide is encoded on the FMRFamide precursor of the snail Helix aspersa but does not activate the FMRFamide-gated sodium current

The complete sequence of the FMRFamide precursor cDNA from Helix aspersa is reported here. Since the 5' end of this cDNA is identical to that of the precursor that encodes the heptapeptide analogs of FLRFamide, the two transcripts are probably derived by alternative RNA splicing. A novel pentapeptide, Glp-Phe-Tyr-Arg-Phe-NH2 (pQFYRFamide), predicted from the cDNA sequence, was purified from extracts of H. aspersa ganglia and identified by mass spectroscopy. Partial gene sequences for the FMRFamide precursors of two closely related pulmonate species-Cepaea nemoralis and Polydontes acutangula-were also determined and compared with the cDNA sequence of H. aspersa and a partial gene sequence previously determined from H. pomatia. Not only are the FMRFamide-related sequences and proteolytic processing sites conserved, but the linear arrangement of these landmarks is also retained. Synthetic pQFYRFamide has some effects on the isolated heart and on neuronal potassium currents in H. aspersa that are similar to those of FMRFamide, but it does not activate the neuronal FMRFamide-gated sodium channel.

Characterization and solubilization of the FMRFamide receptor of squid

The optic lobe of squid (Loligo pealei) contains FMRFamide receptors that can bind an iodinated FMRFamide analog: [125I]-desaminoTyr-Phe- norLeu-Arg-Phe-amide ([125I]-daYFnLRFa). Radioligand binding assays revealed that squid FMRFamide receptors are specific, saturable, high affinity sites (Kd = 0.15 nM) densely concentrated in optic lobe membranes (Bmax = 237 fmole/mg protein). The receptors appeared to be coupled to Gs because guanine nucleotides inhibit receptor binding and the stimulation of adenylate cyclase by FMRFamide is GTP-dependent. Both the binding and cyclase data showed that FMRFamide, but not FMRF-OH, interacts at FMRFamide receptors; thus the C-terminal Arg-Phe-amide is critical for binding. The high binding affinity of FMRFamide (0.4 nM IC50) was specific for FMRFamide-like peptides. The structure-activity relations of many FMRFamide analogs were defined in detail and were nearly identical for both the membrane-bound and detergent-solubilized receptors. We also found that squid optic lobe contains FMRFamide-like reactivity as measured with both a radioimmunoassay and a radioreceptor assay. Moreover, we have sequenced a fragment of genomic DNA that encodes a FMRFamide precursor. Our findings in sum suggest that FMRFamide is a neurotransmitter in squid optic lobe, and that this tissue is a good source from which to purify FMRFamide receptors.

FMRFamide-related peptides from the kidney of the snail, Helisoma trivolvis

Three FMRFamide-related peptides (FaRPs) were purified and characterized from the kidney of the snail, Helisoma trivolvis, by HPLC and detected using two radioimmunoassays (RIA) for FaRPs. Automated sequencing and mass spectrometry of the isolated peptides suggest the following sequences: Phe-Met-Arg-Phe-NH2 (FMRFamide), Phe-Leu-Arg-Phe-NH2 (FMRFamide), and Gly-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (GDPFLRFamide). The FaRPs, predominantly the heptapeptides, were also detected by HPLC and RIA in other osmoregulatory tissues such as the skin, mantle, and the hemolymph. The level of FaRPs, detected by radioimmunoassay, appears to be lower in snails kept under hyposmotic stress than in snails kept under isosmotic stress. The FaRPs appear to be involved in osmoregulation in H. trivolvis.

SCP-Related Peptides From Bivalve Mollusks: Identification, Tissue Distribution, and Actions

The SCPs3 are a small peptide family, characterized in gastropods, and implicated in the control of the cardiovascular system and the muscles involved in feeding and gut motility. We aimed to determine the manifestation of this peptide family in the class Bivalvia. Acetone extracts of whole bivalves were fractionated by high pressure liquid chromatography (HPLC), and reactive peaks were identified by radioimmunoassay (RIA). After purification, sequencing, and analysis by mass spectroscopy, three peptides were identified in the clam Mercenaria mercenaria: IAMSFYFPRMamide, AMSFYFPRMamide, and YFAFPRQamide4. SCP-related peptides from two other species were also sequenced: APKYFYFPRMamide and SAFYFPRMamide from an oyster, Crassostrea virginica; and AMSFYFPRMamide (identical to one of the clam peptides) from a cockle, Dinocardium robustum. The tissue distribution and pharmacological actions of the clam SCPs were determined in M. mercenaria, as follows. The levels of peptide in extracts of 12 tissues were estimated by RIA. The largest concentrations of SCP occur in the palps and the visceral ganglia; the levels in the cerebral and pedal ganglia, the rectum, intestinal typhlosole, and gills were substantially lower; and the smallest amounts were found in the heart and the style sac typhlosoles. Immunohistochemistry revealed many cell bodies in the periphery of the ganglia and fibers in the neuropil. Immunoreactive, varicose fibers also occur in the typhlosoles of the intestine and style sac, and in the rectum, gill, and palps. The atrioventricular valves, but not the atria or ventricle proper, contain immunoreactive fibers. Synthetic clam SCPs were assayed on the rectum, the typhlosoles of the intestine and style sac, and the ventricle, all isolated in an organ bath. At low to moderate doses, the SCPs relaxed the muscles of the rectum; higher doses had biphasic actions. The muscles of the intestinal and style sac typhlosoles were relaxed, and spontaneous rhythmicity was slowed by the SCPs. Most ventricles were unresponsive. We conclude that the SCPs isolated in bivalves--though distinctive--are true homologs of those in gastropods. Moreover, the bivalve peptides also serve similar roles, controlling feeding and digestion, and perhaps even cardioactivity.

The Sequences of Five Neuropeptides Isolated from Limulus using Antisera to FMRFamide

Five neuropeptides were isolated from CNS extracts of the horseshoe crab Limulus polyphemus by high pressure liquid chromatography (HPLC). The peptides were identified by radioimmunoassays (RIAs) based on two antisera raised to FMRFamide-related peptides (FaRPs). The purified peptides were analyzed by automated sequencing and mass spectrometry, and the following sequences were obtained: DEGHKMLYFamide, GHSLLHFamide, PDHHMMYFamide, DHGNMLYFamide, and GGRSPSLRLRFamide. The first four peptides are members of a novel family with virtually no relationship to FMRFamide. GGRSPSLRLRFamide, on the basis of structural similarity, becomes the second member of a class of FaRPs known previously only from a peptide isolated from mosquito heads. At least one member of the novel family (GHSLLHFamide) inhibits the isolated heart of Limulus.