Juiirnal of Neui’odiemisfry. 1976,
Val. 26, pp. 335-343. Pegamon Press Prmtsd in Great Brltain.
THE UPTAKE OF BIOGENIC MONOAMINES BY THE ISOLATED AURICLE OF THE SNAIL ( H E L I X POMATJA) L. HIRIPI,’V. NEUHOFF and N. N. OSBORNE Max-Planck-Institut fur experimentelle Medizin, Forschungsstelle Neurochemie, 3400 Gottingen, Germany (Received 28 May 1975. Accepted 21 July 1975)
Abstract-The uptake of [3H]5HT, C3H]dopamine, [3H]noradrenaline and [3H]octopamine into the auricle of Helix pomatia was studied. When tissues were incubated at 25°C in media containing radioactive amines, tissue: medium ratios of about 49:1, 14:l and 5 : l for 5-HT, dopamine. noradrenaline, and octopamine respectively were obtained after a 2G30 min incubation time. Tissues incubated at 25°C in media containing radioactive amines for 2G-30 mins showed that almost all (96%) the radioactivity was present as unchanged C3H]5HT, C3H]dopamine, C3H]octopamine or [3H]noradrenaline. The high tissue:medium ratios for 5-HT and dopamine, but not for noradrenaline and octopamine, showed saturation kinetics which were dependent upon temperature and sodium ions. From the Lineweaver-Burk plots, two uptake mechanisms for 5-HT at 25°C were resolved; the high affinity uptake process having a K,, value of 6.0 x lo-* M and a Vmt value of 0,115 nmol/g/min while the lower affinity process had a Km2 value of 1.04 x 1 0 - 6 ~and a Vm2 value of 0.66nmol/g/min. At 0°C a single uptake mechanism for 5-HT occurred which gave a K , value of 502 x M and a V, value of 0.0165nmol/g/min. In the case of dopamine, the Lineweaver-Burk plot at 25°C showed a single uptake process with values for K , and V, of 1.55 x 10 ~’ M and 0.086 nmol/g/min respectively. This process did not function at 0°C. The effect of various agents and ions upon the accumulation processes for all amines was also studied, and the data indicate that the same neurons probably accumulate more than one amine type. It is concluded that 5-HT and dopamine uptake in the auricle is a mechanism for inactivating these substances at 25°C and that an uptake mechanism for 5-HT also functions at 0°C. The results are discussed from the point of view of 5-HT’s being the cardioexcitatory substance in the snail heart.
SUBSTANTIAL amounts of 5-HT (5-hydroxytryptamine) the snail heart, it is important to show that a and dopamine occur in the snail nervous system and mechanism exists for their inactivation. There is little the data available suggest that both amines function monoamine oxidase activity in the snail heart (GUTHas neurotransmitters in gastropods (GERSCHENFELD,RIE et al., 1975), and all the available data show the et al., 1973; KERKUT,1973; WELSH, 1972; COTTRELL & amines to be degraded very slowly (OSBORNE MACON,1974; OSBORNE,1974 u o r b). These two 1973, 1975a). Since it is now clear that reuptake of amines and noradrenaline also exist in the snail heart the released transmitter substance is a way of inacti(OSBORNE & C O ~ E L L1970; , HIRIPI& SALANKI, vating them in vertebrates (IVERSEN,1970, 1971; 1973; COTTRELL & OSBOKNE, 1969),and although they SNYDERet a/., 1973), it is possible that such all excite the isolated heart (COTTRELL & OSBORNE,mechanisms may also exist in the snail. Autora1969), evidence favours serotonin as the cardioexcita- diographic studies have shown that certain nerves in tory substance (RozsA & PER~NYI, 1966; WELSH, the molluscan heart are capable of accumulating 1971). However, the possibility that the two catechol- radioactive 5-HT (TAXI& GAUTRON,1969) and amines also have transmitter functions in the heart studies of TVERSEN & ASHER (1970) have demonstrated cannot be excluded, and moreover, since octopamine the same process in Aplysia heart. The snail heart has recently been discovered in defined molluscan (auricle, ventricle or whole heart) would seem a parneurons (SAAVEDRA et al., 1974), the question arises ticularly good preparation for analysing uptake whether this amine also exists in the snail heart, and mechanisms of substances since this organ lies within a blood sinus and is not penetrated by vessels. Thereif so, whether it has a specific role. In order to decide whether serotonin or the other fore incubation of the snail’s thin-walled auricle in biogenic monoamines have transmitter functions in a n artificial medium in uitro would be less unphysiological than incubation of vertebrate tissues. The aim of the present work was to find out whether the auriPermanent address: The Biological Research Institute cle of Helix pomatia accumulates serotonin, dopaof the Hungarian Academy of Sciences, Tihany, Hungary. mine, noradrenaline and octopamine, and if so, to uc. ?hi2