Cardiac regulation by endogenous small cardioactive peptides and FMRFamide-related peptides in the snail Helix aspersa

The putative hepatopeptide pQDPFLRIamide, previously known only from its appearance in a cDNA clone from Helix aspersa, was isolated from circumoesophageal ganglia extracts and sequenced. Extracts of several tissues were fractionated by high performance liquid chromatography and the fractions analysed by radioimmunoassay (RIA). The results indicate that ten cardioactive peptides, FMRFamide, FLRFamide, six FMRFamide-related heptapeptides and two nonapeptide analogues of the small cardioactive peptides (SCPs), are present in the circumoesophageal ganglia (brain), the visceral nerve trunk (from which the cardiac nerve branches) and the aorta. The heart contains the two tetrapeptides, FMRFamide and FLRFamide, and the SCPs, but the heptapeptides were completely undetectable in this organ. The levels of tetrapeptide were high enough to allow their calcium-dependent release from the heart to be demonstrated. Immunohistochemistry revealed a diffuse SCP and FMRFamidergic innervation distributed throughout the heart. These data support the idea that, although the ten peptides are probably acting as neurotransmitters throughout most of the cardiovascular system, the heptapeptides probably also have a neurohormonal role on the Helix aspersa heart itself. The binding affinities of the various antisera used in these studies were examined in competitive RIAs, in non-competitive dot-blot assays or in both.

Phe-Met-Arg-Phe-NH2 (FMRFa)-related peptides inhibit Na(+)-Ca2+ exchange in cardiac sarcolemma vesicles

The molluscan cardioexcitatory tetrapeptide FMRF-amide (Phe-Met-Arg-Phe-NH2) and related peptides inhibit Na(+)-Ca2+ exchange in calf cardiac sarcolemma vesicles. FMRFa itself has a low inhibitory potency (IC50 = 750 microM) which completely resides in its COOH-terminal RFa portion. The physiologically active analog FLRFa is 10-fold more potent (IC50 = 60 microM). Two other substitutions of the Met2 in FMRFa, by either Ile or Lys increase inhibitory potency 7- and 50-fold, respectively. The inhibitory potency increases 300-500-fold if the NH2-terminal Phe1 in FMRFa is substituted by either Val or His (IC50 = 1-2 microM). The inhibitory activity of WnLRFa (IC50 = 40 microM) is lost when either the NH2-terminal amino group is acylated or the NH2-terminal Trp1 is deleted. These data suggest that the COOH-terminal portion is essential for the basic low potency inhibition of Na(+)-Ca2+ exchange, whereas the NH2-terminal portion is important for the potentiation of the inhibitory activity. Although the IC50 values of various peptides range widely (10(-6)-10(-3) M), all of them induce a complete inhibition. The dose-response pattern of the peptide-induced inhibition is identical for the Na(+)-Ca2+ exchange and its partial reaction, the Ca(2+)-Ca2+ exchange. The inhibitory effect is reversible and affects both Nai(or Cai)-dependent 45Ca uptake and Nao-dependent 45Ca efflux, suggesting that the bidirectional movements of ions are altered. A mild pretreatment of vesicles with trypsin augments the Na(+)-Ca2+ exchange 1.5-fold but diminishes the inhibitory potency 3-4-fold, suggesting that the inhibition is mediated by an extravesicular membrane protein. The characteristics of the peptide-induced inhibition resemble the effect of opiates on Na(+)-Ca2+ exchange. FLRFa and dextrorphan (a non-opioid stereoisomer of an opiate agonist) are mutually exclusive inhibitors, suggesting that they may bind to the same site. This putative site lacks the pharmacological properties of opiate receptors and may be located either on the Na(+)-Ca2+ exchanger or at its vicinity. Endogenous analogs of FMRFa may regulate intracellular calcium via Na(+)-Ca2+ exchange.

The localization of FMRFamide in the nervous and somatic tissues of Nereis virens and its effects upon the isolated esophagus

1. The tetrapeptide FMRFamide which is present in extracts of Nereis virens was localized in various nereid tissues immunohistochemically. 2. Immunoreactive FMRFamidergic cells and fibers were found in the supraesophageal (brain) and subesophageal ganglia, as well as in the intersegmental ganglia of the ventral nerve cord. Immunoreactive fibers were present in the neuropile of, and the connectives between, the supraesophageal, subesophageal, and intersegmental ganglia. 3. In the periphery immunoreactive FMRFamidergic fibers and a few cell bodies were observed in the gut. Sparse fibers were also seen in the body wall, parapodia, and cephalic palps. When the antiserum was preabsorbed with FMRFamide, no specific immunoreactivity was detected. 4. The esophagus of Nereis, isolated and suspended in a tissue bath, responded to FMRFamide with a dose-dependent relaxation; threshold was between 30 and 300 nM, and the EC50 was 1.55 +/- 0.60 microM. Benzoquinonium did not modify this response. 5. Thus, FMRFamide seems to be a neurotransmitter in both the central and peripheral nervous system of Nereis virens, and may be involved in the control of esophageal motility.

Characterization of Two Novel Neuropeptides From the Sea Cucumber Holothuria glaberrima

Two peptides were purified from intestinal extracts of a sea cucumber, Holothuria glaberrima, by high pressure liquid chromatography (HPLC). The peptides were detected by a radioimmunoassay (RIA) based on an antiserum raised to the molluscan peptide, pGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide). Automated sequencing and mass spectrometry indicate that the isolated peptides are: Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide). These are the first peptides to have been isolated from a member of the echinoderm class Holothuroidea. The antiserum used in the RIA of the peptides was also employed in localizing immunoreactive nerve cells and fibers in the intestine of H. glaberrima. The immunohistochemical results suggest that these peptides might be responsible for the FMRFamide-like immunoreactivity reported earlier. Sequence similarities between GFSKLYFamide, SGYSVLYFamide, and a pair of peptides previously isolated from starfish lead us to propose that all four molecules are members of a family of peptides acting as neurotransmitters in echinoderms.

Relationships among the FMRFamide-like peptides

The nuclear family of FaRPs (comprising those peptides that are, on compelling evidence, homologous) appears to be restricted to the protostome invertebrate phyla: i.e. Mollusca, Arthropoda, Annelida and Nematoda. Neither the origin nor the range of the family has been definitively established. That is, no genuine homologs have been demonstrated yet in the flatworms (though not for lack of trying), and neither the pseudocoelomate phyla related to the nematodes, nor the coelomate relatives of the annelids have been examined. The extended family of FaRPs (including peptides with little consistent sequence similarity beyond a penultimate Arg and an amidated hydrophobic residue at the C-terminal) exists in all phyla. Such a superfamily was probably first proposed by Morris et al. (1982), whose sequencing of SCPB suggested to them a class of peptides, "... the key unit for biological activity being Phe-A-Arg-B-amide (where A and B are also hydrophobic amino acids)." The ubiquity of the convergent FaRPs could reflect a conserved family of complementary heptahelical receptors requiring the arginyl residue for binding (Price and Greenberg, 1989). But another selective advantage would be the protection provided by a penultimate Arg against certain deamidating peptidases, found so far in yeast and mammals (Jackman et al., 1990).

Seven FMRFamide-related and two SCP-related cardioactive peptides from Helix

Pulmonate snails have a more complex array of cardioexcitatory peptides than other molluscs, and Helix has a more complex array than most other pulmonates. Since a full characterisation of the cardioexcitatory peptides is necessary for an understanding of physiology, we sought to identify the members of two families of such peptides - the small cardioactive peptides (SCPs) and the FMRFamide-related peptides (FaRPs) - from Helix aspersa. We characterised the peaks of immunoreactivity from HPLC both by their elution times and by their molecular weights as determined by fast atom bombardment mass spectrometry (FABms). These two criteria, used in parallel, facilitated our identification of several known peptides: MNYLAFPRMamide, identical to SCPB of Aplysia; two tetrapeptide FaRPs, FRMRamide and FLRFamide; and three hepatapeptide FaRPs, NDPFLRFamide, SDPFLRFamide and pQDPFLRFamide. Of these peptides, only FMRFamide and pQDPFLRFamide have previously been reported from Helix. We also discovered an additional SCP and two novel FaRPs and sequenced them. The SCP is Ser-Gly-Tyr-Leu-Ala-Phe-Pro-Arg-Met-amide (SGYLAFPRMamide), and the heptapeptide FaRPs are Asn-Asp-Pro-Tyr-Leu-Arg-Phe-amide (NDPYLRFamide) and Ser-Glu-Pro-Tyr-Leu-Arg-Phe-amide (SEPYLRFamide). When these nine peptides were tested on isolated Helix ventricles, the SCPs were the most potent cardioexcitors, the heptapeptide FaRPs were next, and the tetrapeptides had the least activity.

Further characterization of Helix FMRFamide receptors: kinetics, tissue distribution, and interactions with the endogenous heptapeptides

The biphasic binding of 125I-daYFnLRFamide to crude brain membranes of Helix aspersa is due to two discernible sites (high and low affinity) rather than different agonist-induced states. The tissues in the snail that show the greatest specific 125I-daYFnLRFamide binding are the brain, reproductive system, and digestive system. The heart shows moderate binding levels, whereas low values are obtained in the oviduct and retractor muscles. The N-terminal SAR of the Helix heptapeptides (X-DPFLRFamide) indicates that, although the substitution of Leu for Met accounts for some, the dipeptide X-Asp produces most of the loss in potency at FMRFamide receptors in Helix brain.

Vasectomy technique

Vasectomy is a safe and effective method of male sterilization. The procedure and necessary follow-up care can usually be performed in an office setting. Failure of the procedure may be due to incorrect identification of the vas, recanalization or presence of an accessory vas.

The identification, localization, and pharmacology of FMRFamide-related peptides and SCPB in the penis and crop of the terrestrial slug, Limax maximus

1. The molluscan neuropeptides FMRFamide, pQDPFLRFamide, and SCPB were tested on the isolated crop and penis of the terrestraial slug, Limax maximus. FMRFamide and pQDPFLRFamide stimulated the penis and inhibited contractions of the crop. In contrast, SCPB either stimulated or relaxed the penis and increased the tone of the crop. 2. Fibers and varicosities containing immunoreactive (ir-) FMRFamide and ir-SCPB were located in the penis and crop. 3. Extracts of penes, crops, ganglia, and whole animals all contained FMRFamide, FLRFamide, SDPFLRFamide, NDPFLRFamide, and pQDPFLRFamide. 4. These results suggest that the FMRFamide-related peptides and SCPB are involved in the regulation of the reproductive and digestive activities of Limax.

Prison medicine

Prisoners in U.S. correctional facilities constitute a unique patient population in need of health services. Physicians who provide medical services to inmates also must interact with prison officials. Drug withdrawal, self-destructive behavior and infectious diseases, including acquired immunodeficiency syndrome, are a few of the challenges to be met.

Relationships between the FMRFamide-related peptides and other peptide families

The relationships between peptide families are recognized in terms of structural similarity and immunological and biological activity. Most of the currently known FMRFamide-related peptides (FaRPs) of molluscs were tested in a radioimmunoassay (RIA) and in the two standard bioassays for FMRFamide: the radula protractor muscle of the whelk Busycon contrarium, and the isolated heart of the clam Mercenaria mercenaria. Some peptides were also tested on the heart of the snail Helix aspersa. The responses of the different assays to these peptides were generally similar, but substantial diversity precluded an absolute resolution of relationships, even among molluscan FaRPs. Nevertheless, this set of responses does constitute a standard against which to estimate the relative affinities of putative FaRPs from other animal groups. Many of the non-molluscan FaRPs (e.g., the pancreatic polypeptide-related peptides, gastrin/CCK, and the opioid peptides) are relatively inactive on the molluscan assays, but others (e.g., LPLRFamide, a peptide isolated from chicken brain; the opioid receptor-modulating peptides A18Fa and F8Fa; and gamma 1-MSH) were relatively potent. Several arthropod FaRPs have substantial FMRFamide-like sequence similarity and immunoreactivity, and they may be homologous members of the molluscan peptide family. However, those structural and functional aspects of peptide families that transcend phyletic lines probably reflect basic principles of binding between peptides and membrane proteins rather than homology.

John Henry Welsh: his years, works and flock

John H. Welsh came down from Boothbay, Maine in the late twenties and landed at Harvard. There he launched his academic career, raised a family, raised an additional family of graduate students and postdoctoral associates, and (with them all) shaped and cultivated diurnal rhythmicity, the biology of neurosecretion, and comparative neuropharmacology. After about 45 yr in the vineyards of Cambridge, he returned to Boothbay and his garden, tree-farm, grandchildren, writings and other good works.

The actions of FMRFamide-like peptides on visceral and somatic muscles of the snail Helix aspersa

Phe-Met-Arg-Phe-NH2 (FMRFamide) and pyroGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide) occur in the ganglia and tissues of the snail, Helix aspersa. This report describes the effects of these two neuropeptides on five visceral organs or somatic muscles isolated from the snail (Table 1). The epiphallus, as well as the rest of the male reproductive tract, was contracted by both FMRFamide and pQDPFLRFamide, and the threshold was usually below 5 X 10(−9) mol l-1 (Fig. 1). Both peptides also reduced the resting tone of the crop and decreased the force and frequency of its rhythmic activity; FMRFamide is about 10 times more potent (Fig. 4). In contrast, pQDPFLRFamide was about 100 times more potent than FMRFamide as a cardioexcitatory agent (Fig. 5). The actions of the peptides on the pharyngeal and tentacle retractor muscles were markedly different: FMRFamide primarily contracted these muscles; and pQDPFLRFamide usually had no effect alone, but relaxed or diminished contractions induced by FMRFamide and acetylcholine (ACh) (Figs 6, 8, 9). Other analogues of FMRFamide were tested, but none was as effective a relaxing agent as pQDPFLRFamide. The effects of FMRFamide and pQDPFLRFamide on all of the preparations could be distinguished from those produced by ACh and 5-hydroxytryptamine (5-HT); thus the actions of the neuropeptides were not mediated by cholinergic or serotonergic neurones. The stimulation of the musculature in the male reproductive tract and the inhibition of motility of the digestive system by FMRFamide and pQDPFLRFamide implicate these peptides in the control of reproductive behaviour. The effectiveness of pQDPFLRFamide in relaxing the retractor muscles and as a cardioexcitatory agent led to the hypothesis that this heptapeptide and FMRFamide, acting at distinct receptors, cooperate to regulate the excitability and contractility of the snail's musculature between the extremes of aestivation and active locomotion.

Evidence for a novel FMRFamide-related heptapeptide in the pulmonate snail Siphonaria pectinata

Extracts of whole false limpets (Siphonaria pectinata) were analysed to determine their complement of FMRFamide-related peptides. As in other pulmonates, FMRFamide itself was found to account for only a portion of the immunoreactivity; the largest immunoreactive peptide peak eluted during HPLC under acidic conditions at the same position as a peak also found in other pulmonates. This major peak was resolved into two components by HPLC at neutral pH, and one component was identified as the heptapeptide amide, GDPFLRFamide, previously described from Lymnaea. The amino acid composition of the second component indicates that it is also a heptapeptide, but that it has two Asx (aspartic acid or asparaginyl) residues instead of the one found in the previously identified pulmonate heptapeptides.

The brain of Lymnaea contains a family of FMRFamide-like peptides

Authentic FMRFamide and two FMRFamide-related heptapeptides were purified from the central nervous system of the fresh water snail Lymnaea stagnalis. The sequences of the heptapeptides were determined as: Ser-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (SDPFLRFamide) and Gly-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (GDPFLRFamide) by modified Edman degradation and enzymatic digestion. Relatively high quantities of the deamidated and therefore non-immunoreactive analogs of these two peptides (SDPFLRF and GDPFLRF) were also found. SDPFLRFamide and GDPFLRFamide were synthesized and were found to be chromatographically and biologically indistinguishable from the natural peptides, confirming the sequences. The log dose-response curves for the chronotropic action of either synthetic peptide on the heart of Lymnaea was very similar to that of FMRFamide. These data indicate that Lymnaea contains a family of FMRFamide-like peptides.

Cross-phyletic bioactivity of arthropod neurohormones and molluscan ganglion extracts: evidence of an extended peptide family

Two structurally related arthropod neuropeptides, red pigment concentrating hormone (RPCH) and adipokinetic hormone (AKH), are potent excitors of the heart of the clam Mercenaria mercenaria. The response is bimodal: whereas the threshold for affected hearts is 1-3 X 10(-9) M, about 40% of the preparations are virtually unresponsive. Aqueous extracts of Mercenaria ganglia contain a substance which concentrates the red pigment in the erythrophores of intact destalked Uca pugilator and even of its isolated legs. This substance is retained on Sephadex G-15 and co-elutes with synthetic shrimp RPCH. The active fractions also concentrate the erythrophores and the leucophores of destalked shrimp (Penaeus). Neither dopamine nor the molluscan neuropeptide FMRFamide had any chromatophorotropic effect in these assays. The activity of the ganglion extracts was abolished by digestion with chymotrypsin. In conclusion, molluscan ganglion extracts contain a peptide factor, possibly an analog of RPCH, that concentrates the pigments of crustacean chromatophores by a direct action on the cells.

Cardiovascular effects of intraventricular injection of FMRFamide, Met-enkephalin and their common analogues in the rat

The molluscan neuropeptide, Phe-Met-Arg-Phe-NH2 (FMRFamide), the mammalian opioid peptide met-enkephalin, and their common analogues, met-enkephalin-Arg6-Phe7 (YGGFMRF) and Tyr-Gly-Gly-Phe-Met-Arg-Phe-amide (YGGFMRFamide), were injected into the lateral ventricle of the rat; the cardiovascular effects were studied. FMRFamide caused a rapid, transient elevation in blood pressure accompanied by a great increase in pulse pressure. These effects were followed by secondary increases in blood and pulse pressures. Met-enkephalin produced an initial reduction in blood pressure which was followed by a gradual increase at the higher of two test doses (300 nmole). Injection of YGGFMRF resulted in a gradual increase in blood pressure. This response resembled that to met-enkephalin. The initial response to YGGFMRFamide was similar to that to FMRFamide: increases in both blood and pulse pressures after injection. However, the secondary effect of YGGFMRFamide, a prolonged reduction in blood pressure, was not produced by FMRFamide. These results suggest that the initial excitatory cardiovascular responses may be due to the presence of the C-terminal amide. All of the cardiovascular effects of injecting these peptides into the lateral ventricle were abolished by pre-treatment with naloxone in a dose that, itself, produced no cardiovascular changes. In conclusion, these peptides seem to act via the naloxone sensitive opiate receptors in the rat brain.

THE FMRFamide-LIKE NEUROPEPTIDE OF APLYSIA IS FMRFamide

The head ganglia from 350 Aplysia brasiliana were extracted and purified by gel (Sephadex G-15) and cation exchange (CM-Sephadex) chromatography; the fractions were examined with radioimmunoassays (RIA) for the molluscan neuropeptides, FMRFamide and SCP_B. Immunoreactive (ir-) FMRFamide (but not ir-SCP_B) coeluted with authentic FMRFamide from both chromatographic columns. The amino acid composition of the purified peptide was: Phe 2: Arg 1: Met 1. Digestion of purified ir-FMRFamide with carboxypeptidase Y indicated that the four residues were in the same sequence as occurs in FMRFamide. The dose-response curves for purified and synthetic FMRFamide on the radula protractor muscle of Busycon contrarium were coincident, as were their inhibition binding curves in the FMRFamide RIA. The highest concentrations of ir-FMRFamide were in the pedal and pleural ganglia; but SCP_B was concentrated in the buccal ganglion. Synthetic SCP_B has no effect on the radula protractor muscle of Busycon or the isolated heart of Mercenaria. In conclusion, the FMRFamide-like peptide in the gastropod Aplysia is FMRFamide, so this peptide has now been identified in two molluscan classes. Moreover, the proposed structural relationship between FMRFamide and SCP_B is fortuitous, and these two peptides should have different physiological functions in Aplysia.

The molluscan neurosecretory peptide FMRFamide: comparative pharmacology and relationship to the enkephalins

The molluscan neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) has diverse actions on excitable tissues of molluscs, including hearts, noncardiac muscles, complex organs, and neurons. The intracellular transducing mechanisms are also diverse and are not readily correlated with particular responses. FMRFamide increases cyclic AMP levels concomitant with both cardioexcitation and inhibition, but not with muscle contraction. In the same tissues, the effects of 5-hydroxytryptamine are dissimilar and are always accompanied by a cyclic AMP increase. FMRFamide and acetylcholine cause similar tonic contractions of the Busycon radula protractor muscle and identical catch contractures of the mytilid anterior byssus retractor muscle, but the ionic basis of excitation and the sources of activator calcium for contraction are not the same for the two agonists. A comparative study of structure-activity relations showed that FMRFamide receptors are heterogeneous. Helix aspersa ganglia contain no FMRFamide, but a close analog occurs and has been tentatively identified. Evidence supporting a proposed homology between FMRFamide-like and opioid peptides is summarized. The effects of the amphiactive heptapeptide Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2 on the venus clam rectum support this hypothesis.

Competitive inhibition by dimethylsulfoxide of molluscan and vertebrate acetylcholinesterase

Anticholinesterase-like effects of dimethylsulfoxide (DMSO) were demonstrated on a variety of invertebrate muscles. The excitatory effects of acetylcholine (ACh) on the isolated preparations of the Geukensia demissa heart and anterior byssus retractor muscle (ABRM), and of the Busycon contrarium radula protractor muscle, were potentiated by DMSO (1-5 microliters/ml; 1 microliter/ml = 14 mM). The negative chronotropic effects of ACh, but not of 4-ketoamyltrimethylammonium, were potentiated by DMSO (1-5 microliters/ml) on the isolated heart of the oyster Crassostrea virginica. These four muscles have acetylcholinesterase enzymes of high activity. In contrast, Mercenaria mercenaria hearts have weak cholinesterase activity, and the effects of ACh on this isolated myocardium were not potentiated by DMSO (2-20 microliters/ml). DMSO (0.1-15 microliters/ml) was a competitive inhibitor of both a crude preparation of oyster heart acetylcholinesterase (AChE) (the Km increased 24-fold with DMSO at 15 microliters/ml; the I50 was 1.3 microliters/ml DMSO when [ACh] = Km) and a purified Electrophorus AChE (the Km increased 4.5-fold when DMSO was 10 microliters/ml; the I50 was 10 microliters/ml DMSO near [ACh] = Km). The same doses of DMSO were needed to potentiate the pharmacological effects of ACh on the oyster heart, as to inhibit the AChE of this tissue.

A comparison of the cholinesterases of an oyster (Crassostrea virginica) and a clam (Macrocallista nimbosa)

Cholinesterase activities in the hearts and ganglia of an oyster (Crassostrea virginica) and a venerid clam (Macrocallista nimbosa) were measured and compared. Tissue extracts were partially purified by ammonium sulfate fractionation followed by gel column chromatography. Enzymatic activity was assayed spectrophotometrically; substrates were acetyl-, butyryl-, and propionylthiocholine (ATC, BTC, PTC). Kinetic constants characterizing each enzyme were derived. At all substrate concentrations, the hydrolysis rates of both clam enzymes were in the order: BTC greater than PTC greater than ATC. With oyster enzymes the ranking was ATC greater than or equal to PTC greater BTC. The specific activities of oyster heart and ganglion enzymes were similar. In contrast, clam ganglion extracts were 75-100 times more active than clam heart extracts and, with any substrate, had greater activity than either oyster enzyme. All enzyme preparations proved to be homogeneous on the bases of constant substrate activity ratios in successive column fractions, and of intermediate velocities with mixed substrates. Six cholinesterase inhibitors were tested. The specific acetylcholinesterase antagonist, B.W. 62C47, WAS MUCH MORE EFFECTIVE AGAINST OYSTER ENZYMES, WHILE THE SPECIFIC ANTIBUTYRYLCHOLINESTERASE, ISO-OMPA, almost totally inhibited calm enzyme activity, but had little effect on oyster. Eserine was the most effective inhibitor of both enzymes. In conclusion, the enzymes in oyster tissues are acetylcholinesterases, while clam enzymes are butyrylcholinesterases. Nevertheless, clam ganglion esterase is sifficiently active to hydrolyze the physiological substrate, acetylcholine. These results explain the long-observed differences in isolated heart pharmacology between ostreid and venerid bivalves.

Elapid alpha-toxins have no effect on the cholinergic responses of bivalve myocardia

Elapid alpha-toxins (alpha-bungarotoxin, alpha-cobratoxin and crude Bungarus caeruleus venom) do not affect the myocardial nicotinic ACh receptors of the following bivalve molluscs: Mercenaria mercenaria, Chione cancellata, Mya arenaria, Mytilus edulis, Rangia cuneata and Crassostrea virginica.

FMRFamide increases the adenylate cyclase activity and cylic AMP level of molluscan heart

FMRFamide (phenylalanyl-methionyl-arginyl-phenylalanine amide) is a cardioexcitatory peptide recently isolated and identified in molluscan ganglia. Both FMRFamide and 5-hydroxytryptamine (5HT), the cardioexcitatory neurotransmitter in molluscs, were tested on the ventricle of the bivalve Mercenaria mercenaria. Both agents increased myocardial contractility, the intracellular cyclic AMP concentration of intact hearts and the adenylate cyclase activity of a myocardial membrane fraction. FMRFamide was 5--10 times more potent than 5HT. All of the effects of 5HT, and none of those of FMRFamide, were blocked by methysergide, a specific 5HT antagonist.

Synthesis, physicochemical properties, and antitumor activities of analogs of 1-phenyl-3-benzyl-3-methyltriazenes

To study the effect of substituents on the antitumor activities of analogs of 1-phenyl-3-benzyl-3-methyltriazenes, a series of compounds was designed and synthesized in which the substituent on the 1-phenyl was an electron-withdrawing group and the substituent on the 3-benzyl had a broad range of physicochemical properties. Of the 13 analogs prepared and tested against Sarcoma-180 in the mouse, five showed significant activity. The results were submitted to discriminant analysis to determine structure-activity relationships.

Structure of a molluscan cardioexcitatory neuropeptide

A cardioexcitatory substance from ganglia of the clam Macrocallista nimbosa, formerly designated peak C, is the tetrapeptide amide Phe-Met-Arg-Phe-NH2. Its structure was determined by the combined use of Edman dansyl degradation and tryptic digestion. The structure was confirmed by synthesis. This neuropeptide is active at about 10(-8)M when assayed on molluscan muscle.

Purification and characterization of a cardioexcitatory neuropeptide from the central ganglia of a bivalve mollusc

We have purified a cardioexcitatory substance, previously designated peak C, from ganglia of the Sunray Venus clam, Macrocallista nimbosa. Low concentrations (10(-9)-10(-8) M) of this substance not only excite the isolated clam heart, but also produce tonic contractions of the isolated radula protractor muscle of the whelk, Busycon contrarium. These two muscle preparations have therefore been used as a parallel bioassay for peak C. Peak C is inactivated by proteolytic enzymes, has an isoelectric point greater than pH 10 and has an ultraviolet absorption spectrum similar to that of phenylalanine. On thin layer chromatograms, peak C separates into two components; one of these is probably a partially oxidized form produced during purification. Both components react with ninhydrin and with the Sakaguchi reagent for guanidino groups. The amino acid composition of peak C is Phe2.00Met0.81Arg1.12. N-terminal analysis, one round of Edman-dansyl degradation, and tryptic digesting are consistent with the identification of Macrocallista peak C as a tetrapeptide amide: Phe-Met-Arg-Phe-NH2 (FMRFamide).

Use of cluster analysis in the development of structure-activity relations for antitumor triazenes

A series of antitumor triazenes in which the members of the series are physicochemically distinct was designed using the cluster analysis approach as proposed by Hansch and his co-workers. The series that resulted was tested against Sarcoma 180 in the mouse and the antitumor activities were analyzed using regression techniques. The structure-activity relations that resulted are discussed in terms of proposed mechanisms of action.

The localization of acetylcholinesterase and butyrylcholinesterase in the heart, cardiac ganglion and the lateral and dorsal nerves of Limulus polyphemus

Histochemical localization has confirmed that both the heart muscle and the cardiac ganglion along with its branches have cholinesterase activity. Acetylcholinesterase (AChE) is localized in the nerve fibers of the cardiac ganglion and its side (segmental branch) nerves and in the lateral nerves, but AChE could not be demonstrated in the cytoplasm of the ganglionic cell bodies. The dorsal cardioregulatory nerves (segmental cardiac nerves), arising in the central nervous system, also stain intensely for AChE. Butyrylcholinesterase is localized in the cardiac muscle tissue. The presence of intensely staining AChE in the cardiac ganglion and its branches, the lateral nerves and the cardioregulatory nerves sustains the notion that a cholinergic system is involved in the regulation of the Limulus heart.