Abstract. The de novo biosynthesis of linoleic acid [18:2(n-6)], a fatty acid considered to be essential for most animals, was demonstrated in the land snail, Bulimulis alternatus mariae, and the garden slug, Arion circumscriptus.Radiolabeled acetate injected into the animals was incorporated into both 18:2 and 20:2, as demonstrated by radio-high performance liquid chromatography (radio-HPLC) and radio-gas chromatography (radio-GC). GCmass spectrometry (GC-MS) of the methoxy derivatives of the 18:2 and 20:2 isolated from the snail showed that major isomers had the double bonds in the n-6,9 positions. Radio-gas-liquid chromatography (radio-GLC) of the ozonolysis products from the labeled dienoic fatty acid methyl esters showed that both ends of the molecules were labeled, confirming de novo synthesis. The production of linoleic acid by these animals suggests the capability to produce linoleic acid may be widespread in invertebrates. Key words. Linoleic acid biosynthesis; essential fatty acid; A 12 desaturase; Bulimulis alternatus mariae; Arion circumscriptus.Until recently, linoleic acid [ 18:2(n-6)] had been considered to be an essential fatty acid for all animals 3. The requirement for this fatty acid in the animal diet is due to the absence of a A i2 desaturase, the enzyme responsible for the insertion of the second double bond in oleic acid. Plants 4, some fungi 5 and protozoa 6 possess a A 12 desaturase and thus readily produce linoleic acid. Studies in the 1980s demonstrated that many, although by no means all, insect species also possess the ability to produce linoleic acid 7-~°, rendering them free from a dietary requirement of fatty acid. The A 12 desaturase was subsequently characterized in the house cricket 11 and the American cockroach I2. The observation that many insect species could produce linoleic acid suggested the possibility that other invertebrates might also have this capability. The results reported herein demonstrate that the land snail and the garden slug can biosynthesize linoleic acid and suggest that this biosynthetic capability is much more widespread among animals than previously thought. Materials and methodsLand snails, Bulimulis alternatus mariae, were obtained from Carolina Biological Supply Company, Burlington, NC. Garden slugs, Arion circumseriptus, were collected from gardens and marshy areas in Reno, NV. The animals were injected with 1 gCi each sodium [1-14C]acetate (50 ~tCi/mmol), and, after 24 h at room temperature, were killed by freezing at -20 °C. After thawing, lipid was extracted by homogenization in chloroform:methanol:water (1:2:1), and lipids were extracted by the method of Bligh and Dye? 3. Lipid classes were separated by thin layer chromatography (TLC) 7, and fatty acids from polar lipids and triacylglycerols were methylated as described 14. Labeled fatty acid methyl esters were analyzed by radio-HPLC on a Supelco LC-8 reverse-phase column with acetonitrile:water (75:25) as eluant. Radiolabeled fatty acid methyl esters were detected with a Radiomatic Instruments F...

The origin and spread of excitation were visualized with fluo 3 fluorescence in tissues isolated from canine gastric antrum. Sheets of circular muscle (5 × 6 mm) had at least 1 (30%) and up to 3 discrete slow-wave pacing sites located near the longitudinal-circular muscle boundary, whereas similarly sized longitudinal sheets had an average of 5 sites (range 3–12 sites) that initiated Ca2+ waves. Superimposed fluorescent oscillations (circular muscle) and spikes (longitudinal muscle) were seen to initiate and propagate as distinct events, separate from their underlying activities. Average propagation velocities transverse (6–7 mm/s) and parallel (39–45 mm/s) to the long axis of muscle fibers were similar for each type of event in circular and longitudinal tissues; however, distinct regions where velocities of some (but not all) events decreased by up to an order of magnitude were present. The distance propagated by individual events was limited by collisions with concurrent excitable events or recently activated regions. Complex patterns of excitation in gastrointestinal smooth muscle arise as a result of interactions between multiple pacing sites, heterogeneous conduction velocities, and the interplay of adjacent pacemaker domains.

1 The effects of acetylcholine (ACh) on membrane potential, relaxation and cyclic GMP levels were compared to the NO donor L-nitrosocysteine (Cys-NO) in segments of guinea-pig coronary artery.2 ACh and Cys-NO produced concentration-dependent relaxations of muscles contracted with the HI receptor agonist, 2-(2-aminoethyl)pyridine (AEP, 0.35 mM). The relaxation to ACh was unchanged in the presence of NG-monomethyl-L-arginine (L-NMMA; 350 jLM) or indomethacin (3 9LM). 3 Oxyhaemoglobin (HbO; 20 tiM) alone or in combination with L-NMMA increased the EC50 for ACh-induced relaxation whereas relaxation with Cys-NO was almost completely abolished with HbO.4 Scorpion venom (SV; 8.7 pg ml-') increased the EC,0 for relaxation with ACh but not Cys-NO.Combined L-NMMA, HbO and SV produced nearly complete abolition of ACh-induced relaxations. 5 Basal cyclic GMP levels (i.e., 20 pmol mg-l protein) were significantly increased following addition of either ACh (190 pmol mg-' protein) or Cys-NO (240 pmol mg' protein). L-NMMA significantly reduced the rise of cyclic GMP with ACh but not Cys-NO. In contrast, SV did not significantly reduce the rise in cyclic GMP produced with ACh. In the combined presence of L-NMMA and HbO neither ACh nor Cys-NO produced a significant increase in cyclic GMP levels. 6 ACh gave rise to significantly greater membrane hyperpolarization than Cys-NO both in the presence and absence of AEP. Combined L-NMMA and HbO did not reduce the amplitude of hyperpolarization with ACh. 7 These data indicate that some but not all of the actions of ACh in the coronary artery can be mimicked by the NO donor, Cys-NO, suggesting that ACh releases NO as well as a second hyperpolarizing factor (i.e., EDHF). Release of NO results in a large increase in tissue cyclic GMP levels and minimal change in membrane potential whereas release of EDHF results in a large membrane hyperpolarization which is independent of changes in tissue cyclic GMP levels. Both of these pathways appear to contribute to relaxation throughout the entire ACh concentration-relaxation relationship.

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