Predominant accumulation of a 3-hydroxy-γ-decalactone in the male rectal gland complex of the Japanese orange fly, Bactrocera tsuneonis.

The Japanese orange fly, Bactrocera tsuneonis, infests various citrus crops. While male pheromone components accumulated in the rectal glands are well characterized for Bactrocera, but information regarding the chemical factors involved in the life cycles of B. tsuneonis remains scarce. Herein, several volatile chemicals including a γ-decalactone, (3R,4R)-3-hydroxy-4-decanolide [(3R,4R)-HD], were identified as major components, along with acetamide and spiroketals as minor components in the rectal gland complexes of male B. tsuneonis flies. The lactone (3R,4R)-HD was also identified in female rectal gland complexes. The amount of this compound in mature males was significantly higher than those observed in females and immature males. The lactone (3R,4R)-HD was detected in flies fed with sucrose only, indicating that this lactone is not derived from dietary sources during adulthood, but biosynthesized in vivo. The predominant accumulation of (3R,4R)-HD in mature males also suggests a possible role in reproductive behavior.

Attraction and Electrophysiological Response to Identified Rectal Gland Volatiles in Bactrocera frauenfeldi (Schiner).

Bactrocera frauenfeldi (Schiner) (Diptera: Tephritidae) is a polyphagous fruit fly pest species that is endemic to Papua New Guinea and has become established in several Pacific Islands and Australia. Despite its economic importance for many crops and the key role of chemical-mediated sexual communication in the reproductive biology of tephritid fruit flies, as well as the potential application of pheromones as attractants, there have been no studies investigating the identity or activity of rectal gland secretions or emission profiles of this species. The present study (1) identifies the chemical profile of volatile compounds produced in rectal glands and released by B. frauenfeldi, (2) investigates which of the volatile compounds elicit an electroantennographic or electropalpographic response, and (3) investigates the potential function of glandular emissions as mate-attracting sex pheromones. Rectal gland extracts and headspace collections from sexually mature males and females of B. frauenfeldi were analysed by gas chromatography-mass spectrometry. Male rectal glands contained (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro [5.5]undecane as a major component and (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane as a moderate component. Minor components included palmitoleic acid, palmitic acid, and ethyl oleate. In contrast, female rectal glands contained (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and ethyl laurate as major components, ethyl myristate and ethyl palmitoleate as moderate components, and 18 minor compounds including amides, esters, and spiroacetals. Although fewer compounds were detected from the headspace collections of both males and females than from the gland extractions, most of the abundant chemicals in the rectal gland extracts were also detected in the headspace collections. Gas chromatography coupled electroantennographic detection found responses to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane from the antennae of both male and female B. frauenfeldi. Responses to (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane were elicited from the antennae of females but not males. The two spiroacetals also elicited electropalpographic responses from both male and female B. frauenfeldi. Ethyl caprate and methyl laurate, found in female rectal glands, elicited responses in female antennae and palps, respectively. Y-maze bioassays showed that females were attracted to the volatiles from male rectal glands but males were not. Neither males nor females were attracted to the volatiles from female rectal glands. Our findings suggest (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane as components of a sex-attracting pheromone in B. frauenfeldi.

Immunohistochemical colocalization of G protein alpha subunits and 5-HT in the rectal gland of the cartilaginous fish Scyliorhinus canicula.

Serotonin [5-hydroxytryptamine (5-HT)] is an important neuromodulator involved in a wide range of physiological functions. The effects of serotonin are mediated by an extended family of receptors coupled to multiple heterotrimeric G-proteins, associated with cellular membrane. G proteins connect receptors to effectors and thus trigger intracellular signaling pathways. These cellular processes several regulate systemic functions such as embryonic development, gonadal development, learning and memory, and organismal homeostasis. Generally, elasmobranch fish dwell a hypersaline environment and utilize a specialized extrarenal salt secreting organ, the rectal gland, to face ionic homeostasis. In this study in addition to the morphological, histochemical and immunohistochemical description of the Scyliorhinus canicula rectal gland, for the first time, the presence of serotonin (5-HT), and distribution of different types of G protein alpha subunits (Gα o, Gα q/11, and Gα s/olf) has been investigated in the rectal gland epithelium by confocal immunofluorescence techniques. Colocalization G proteins and 5-HT in the secretory epithelium of the gland suggests serotonin acts as a hormone and involves G proteins in an autocrine-paracrine control of rectal gland homeostasis.

Characterisation of C-type natriuretic peptide receptors in the gill of dogfish Triakis scyllia.

Only C-type natriuretic peptide (CNP) has been identified in primitive elasmobranch fish. CNP is the most conserved molecule in the natriuretic peptide family, suggesting that it is the ancestral type. As a first step to investigating the ancestral type of natriuretic peptide receptors, CNP receptors were characterised in an elasmobranch (dogfish, Triakis scyllia) by radioligand-binding analysis using 125I-[Tyr0]-dogfish (df)CNP. None of the modifications of the CNP molecule that occur at the time of iodination (addition of a Tyr residue at the N-terminus, introduction of iodine into Tyr0 or oxidation of Met17) affect the affinity of dfCNP for the receptors. Neither did oxidation of Met17 decrease the ability of CNP to stimulate cGMP production. In the tissues examined, CNP receptors were densest in the gill cells followed by the intestine, interrenal gland and rectal gland, all of which are involved in osmoregulation in elasmobranchs. CNP-stimulated guanylate cyclase (GC) activity was highest in the interrenal gland, intestine, brain and rectal gland, followed by the gill cells. Since the gill cells seem to contain both GC-coupled and uncoupled receptors, this tissue was used to characterise dogfish CNP receptors. Scatchard analysis of the saturation isotherm revealed two classes of binding site: one has a Kd of 24.0 pM and Bmax of 59.9 fmol/mg protein, and the other has low affinity (Kd > 1 nM) and high capacity (Bmax > 200 fmol/mg protein). The higher-affinity binding sites may represent GC-uncoupled receptors, because C-ANF, a specific ligand for GC-uncoupled receptors, almost completely displaced CNP binding. Affinity-labelling experiments showed that dogfish receptors have molecular masses of about 90, 170 and 340 kDa, and CNP binding to the former two receptors is inhibited by C-ANF. After reduction with 2-mercaptoethanol, most 170 kDa labelling was shifted to 90 kDa. It is concluded that GC-uncoupled receptors in the dogfish gill have higher molecular mass than those of mammals and eel (about 65 kDa), and are present mostly as monomers even in non-reducing conditions. However, a small population of GC-coupled receptors is also present, as demonstrated by an increase in cGMP production.

Immunohistochemical evidence for neural mediation of VIP activity in the dogfish rectal gland.

Vasoactive intestinal peptide (VIP) has been shown to increase chloride secretion from the rectal gland of the spiny dogfish, Squalus acanthias. Immunohistochemistry was used to localize the distribution of immunoreactive VIP (iVIP). Rectal glands were perfused with either buffered acrolein or paraformaldehyde/glutaraldehyde, sectioned (20 micron) and processed by either avidin-biotin complex (ABC) or peroxidase anti-peroxidase (PAP) methods. At the light microscopic level, iVIP was observed in thick fibers which traversed the fibromembranous capsule of the rectal gland. In the parenchyma, smaller iVIP-containing fibers were noted within connective tissue and in close approximation to tubule cells. At the ultrastructural level, iVIP axons in the fibromembranous capsule were unmyelinated. Immunoreactive fibers within the parenchyma frequently terminated on the basal side of tubule cells. Within the glands, iVIP bouton terminals were observed and contained vesicles of different sizes, with reaction product in dense core vesicles (60-120 nm). We conclude that iVIP is distributed in nerve fibers throughout the dogfish rectal gland. The anatomic distribution suggests that VIP may act as a neurotransmitter in this model of chloride ion transport.

Evidence of natural hybridization between two sympatric sibling species of Bactrocera dorsalis complex based on pheromone analysis.

Bactrocera carambolae and B. papayae are major fruit fly pests and sympatric sibling species of the B. dorsalis complex. They possess distinct differences in male pheromonal components. In the 1990's, wild Bactrocera fruit flies with morphological traits intermediate between those of B. carambolae and B. papayae were often captured in traps baited with methyl eugenol (ME). Chemical analyses of rectal glands of ME-fed males revealed that the laboratory Fl, F2, and backcross hybrids possessed ME-derived sex pheromonal components ranging from that typical of B. papayae to that of B. carambolae without any specific trend, which included a combination of pheromonal components from both parental species within an individual hybrid. ME-fed hybrids without any ME-derived pheromonal components were also detected. Further chemical analysis of rectal glands from wild Bactrocera males, after ME feeding in the laboratory, showed a combination of pheromonal components similar to that found in the ME-fed, laboratory-bred hybrids. These findings present circumstantial evidence for the occurrence of a natural hybrid of the two Bactrocera species.

Cellular and molecular biology of chloride secretion in the shark rectal gland: regulation by adenosine receptors.

The rectal gland of the dogfish shark (Squalus acanthias) is a sodium chloride secreting epithelial organ whose function was discovered in 1959 by Wendell Burger. The gland, composed of homogenous tubules of a single cell type, is an important model for secondary active chloride transport. Hormonal stimulation of chloride secretion in this system activates asymetrically arranged transport proteins (apical cAMP-activated CFTR-like Cl- channels, basolateral Na/K/2Cl cotransporters, Na/K-ATPase activity, and K+ channels). Five receptors, hormones, and membrane proteins of the shark rectal gland involved in chloride secretion have been cloned recently. Because the intact gland can be perfused via a single artery and vein, it has been possible to examine precisely the metabolic regulation of chloride transport by endogenous adenosine. Rectal gland cells have a high density of both stimulatory A2 type and inhibitory A1 type adenosine receptors. When stimulated by secretagogues, chloride secretion and venous adenosine concentrations increase in parallel, with chloride secretion increasing from approximately 150 to 2100 microEq/hr/g, and adenosine concentrations increasing from approximately 5 to approximately 890 nM. This work of ion transport is accompanied by a marked fall in intracellular ATP activity and a rise in both intracellular AMP and adenosine activity. Agents that prevent the interaction of endogenous adenosine with extracellular receptors significantly increase the chloride transport response to secretagogues. When chloride transport is inhibited by blocking the Na/K/2Cl cotransporter with bumetanide, both adenosine release and chloride secretion fall to basal values. We recently cloned a unique adenosine receptor subtype that is distinct from previously cloned mammalian adenosine receptors. Because of its highly specialized function, single cell type, and simple vascular system, the shark rectal gland is an ideal model system for examining the metabolic regulation of chloride secretion by adenosine receptors.

Properties and function of KCNQ1 K+ channels isolated from the rectal gland of Squalus acanthias.

KCNQ1 (KVLQT1) K+ channels play an important role during electrolyte secretion in airways and colon. KCNQ1 was cloned recently from NaCl-secreting shark rectal glands. Here we study the properties and regulation of the cloned sKVLQT1 expressed in Xenopus oocytes and Chinese hamster ovary (CHO) cells and compare the results with those obtained from in vitro perfused rectal gland tubules (RGT). The expression of sKCNQ1 induced voltage-dependent, delayed activated K+ currents, which were augmented by an increase in intracellular cAMP and Ca2+. The chromanol derivatives 293B and 526B potently inhibited sKCNQ1 expressed in oocytes and CHO cells, but had little effect on RGT electrolyte transport. Short-circuit currents in RGT were activated by alkalinization and were decreased by acidification. In CHO cells an alkaline pH activated and an acidic pH inhibited 293B-sensitive KCNQ1 currents. Noise analysis of the cell-attached basolateral membrane of RGT indicated the presence of low-conductance (<3 pS) K+ channels, in parallel with other K+ channels. sKCNQ1 generated similar small-conductance K+ channels upon expression in CHO cells and Xenopus oocytes. The results suggest the presence of low-conductance KCNQ1 K+ channels in RGT, which are probably regulated by changes in intracellular cAMP, Ca2+ and pH.

Immunodetection of parathyroid hormone-related protein in plasma and tissues of an elasmobranch (Scyliorhinus canicula).

We have used antiserum to human parathyroid hormone-related protein (PTHrP) (1-16) to examine tissues and plasma of the dogfish (Scyliorhinus canicula) for the presence of immunoreactive PTHrP (irPTHrP). The plasma contained high concentrations of irPTHrP (9.34 +/- 0.37 pM), comparable to levels in humans with hypercalcaemia of malignancy. Other tissues with irPTHrP included brain neurones; epithelial cells of the saccus vasculosus, kidney, rectal gland and choroid plexus; and cells of the pituitary pars distalis. PTHrP was not detected in gut, skin, oviduct, and gill epithelia, nor in branchial cartilage. The principal source(s) of plasma PTHrP is not known.

The cellular location of 1 alpha-hydroxycorticosterone binding protein in skate.

Antiserum to 1 alpha-hydroxycorticosterone binding protein was used to investigate its location in selected tissues of the skate Raja ocellata. Immunofluorescence, using an indirect technique, showed 1 alpha-hydroxycorticosterone binding sites in potential target tissue: gill. chloride cells, rectal gland parenchyma, and a portion of the kidney tubule. The binding protein was not detectable in the ventricle or the intestinal spiral valve but was associated with liver parenchyma and interrenal cells. The intracellular location of the binding protein is apparently tissue specific.

Properties of single- and double-barreled Cl channels of shark rectal gland in planar bilayers.

Chloride channels from the apical plasma membrane fraction of rectal gland of Squalus acanthias were characterized by incorporation into planar bilayers in the presence of cAMP-PK/ATP. In a total of 80 bilayer preparations, 21 Cl-selective channels were observed as single channels and 13 as pairs. This was a significantly greater number of double Cl channels than expected from a binomial distribution. The double Cl channels were divided into two groups based on kinetic and voltage-dependent behavior. One group had properties identical to the single channels (gb1) while the other was consistent with a double-barreled channel (gb2) with coordinated activity between proto-channels. The single-channel slope conductances of gb1 and gb2 from -60 to +20 mV with a 250/70 mM KCl gradient were 41 and 75 pS, respectively. With symmetrical 250 mM KCl, the I-V relation of gb1 showed outward rectification with 47.8 +/- 6.6 pS at cis negative potentials and 68.9 +/- 6.1 pS at cis positive potentials. gb1 was open from 70 to 95% at all electrochemical potentials from -80 to +40 mV. gb2 was steeply voltage dependent between -80 and -20 mV. Both gb1 and gb2 were insensitive to Ca (from 100 nm to 1 microM), blocked by 0.1 mM DIDS and highly selective for chloride. These data suggest that double-barreled Cl channels are related to the family of small, outwardly rectifying Cl channels of epithelial membranes.

Identification of a phospholemman-like protein from shark rectal glands. Evidence for indirect regulation of Na,K-ATPase by protein kinase c via a novel member of the FXYDY family.

The Na,K-ATPase provides the driving force for many ion transport processes through control of Na(+) and K(+) concentration gradients across the plasma membranes of animal cells. It is composed of two subunits, alpha and beta. In many tissues, predominantly in kidney, it is associated with a small ancillary component, the gamma-subunit that plays a modulatory role. A novel 15-kDa protein, sharing considerable homology to the gamma-subunit and to phospholemman (PLM) was identified in purified Na,K-ATPase preparations from rectal glands of the shark Squalus acanthias, but was absent in pig kidney preparations. This PLM-like protein from shark (PLMS) was found to be a substrate for both PKA and PKC. Antibodies to the Na, K-ATPase alpha-subunit coimmunoprecipitated PLMS. Purified PLMS also coimmunoprecipitated with the alpha-subunit of pig kidney Na, K-ATPase, indicating specific association with different alpha-isoforms. Finally, PLMS and the alpha-subunit were expressed in stoichiometric amounts in rectal gland membrane preparations. Incubation of membrane bound Na,K-ATPase with non-solubilizing concentrations of C(12)E(8) resulted in functional dissociation of PLMS from Na,K-ATPase and increased the hydrolytic activity. The same effects were observed after PKC phosphorylation of Na,K-ATPase membrane preparations. Thus, PLMS may function as a modulator of shark Na,K-ATPase in a way resembling the phospholamban regulation of the Ca-ATPase.