[2 unusual responses of the myocardium in the frog Rana temporaria to acetylcholine]. / O dvukh neobychnykh otvetakh miokarda liagushki Rana temporaria na atsetilkholin.

When studying seasonal variations in acetylcholine sensitivity of isolated frog ventricle, two forms of unusual responses have been observed: 1) tonic response induced by supermaximal concentration of acetylcholine, and 2) double response to the increasing acetylcholine concentrations with two different threshold and maximum doses (KAch values differ by 1-2 orders). The tonic response is blocked by mytolone. Both effects are of a seasonal nature. Similar pattern of these reactions in frogs and molluscs suggests a possibility of restoration of evolutionary more ancient form of cholinergic response, hormonal influences being involved into this process.

[Seasonal characteristics of the emergence from inhibition by and desensitization to acetylcholine of the frog heart muscle]. / Sezonnaia kharakteristika vykhoda iz tormozheniia i desensitizatsii k atsetilkholinu serdechnoi myshtsy liagushki.

Seasonal changes in the sensitivity to acetylcholine (I/KACh), the time of recovery of half-amplitude (T50), as well as the ACh desensitization were studied in ventricles of the frog Rana temporaria. Cardiac arrest could be induced with 10(-7) to 10(-6) M ACh in winter whereas in spring small rhythmic contractions were observed even at 10(-3) M ACh. A correlation between the heart sensitivity to ACh and the time of the heart beat resuming was found: a decrease in the I/KACh corresponded to the 2-3-fold decrease in the T50 in spring and summer. After repeated ACh application the heart sensitivity decreased by 1.5-2.0-fold, i.e. a desensitization occurred. The data obtained are discussed in respect to the phenomenon of escape and involvement of putative modulators of the cholinergic responses: polyphosphates, lysolecithin, hormones.

[Reciprocal effect of polypeptides and mediators on the ileum of the guinea pig]. / O vzaimnom vliianii polipeptidov i mediatorov na podvzdoshnuiu kishku morskoi svinki.

The cross influence of polypeptides (substance P, eledoisin) and neurotransmitters (acetylcholine, histamine, 5-hydroxytryptamine, ATP) on isolated guinea pig ileum involved a reduction or loss of muscle sensitivity. After the desensitization induced by one of the neurotransmitters the sensitivity of the ileum longitudinal muscle to polypeptides as estimated by the dissociation constant of the drug-receptor complex, decreased, i.e. a non-specific cross desensitization occurred. 5-hydroxytrpyptamine, however, increased the sensitivity to the polypeptides. A similar sensibilizing effect is characteristic of the polypeptides which, after application, increased 1.5-2.0-fold the height of the maximum muscle contraction and decreased 2-4-fold the dissociation constant. A possible involvement of polypeptides not only in their interaction with the target cells but also in the modulation of neurotransmitters, is discussed.

[Changes in the sensitivity of the heart of marine mollusks to acetylcholine during the spawning period]. / Ob izmenenii chuvstvitel'nosti serdtsa morskikh molliuskov k atsetilkholinu v period neresta.

In experiments on 5 species of marine bivalve molluscs (Spisula sachalinensis, Callista brevisiphonata, Mactra sulcatoria, Peronidia venulosa, Mya japonica) it has been shown that the level of sensitivity of cardiac muscle to ACh corresponds to functional condition of the reproductive system. During the discharge of mature sexual products, significant increase in the sensitivity to the mediator is observed -- from threshold ACh concentrations about 10(-9) M to 10(-15)--10(-17) M during spawning. If the spawning time is shifted, the onset of the increase in cardiac sensitivity is shifted as well. This parallelism is absent in species with portional mode of reproduction -- Crenomytilus grayanus and Modiolus difficilis.

[Seasonal changes in myocardial sensitivity to acetylcholine in the molluscs, Anodonta complanata and Anodonta piscinalis]. / Sezonnye izmeneniia chuvstvitel'nosti k atsetilkholinu serdechnoi myshtsy molliuskov Anodonta complanata i Anodonta piscinalis.

Seasonal changes in ACh sensitivity have been studied on isolated cardiac muscle of the bivalve molluscs together with ATP content of the hemolymph and the heart. The lowest ACh sensitivity of the heart was found in August and October (KACh in August was equal to 44.0.10(-6) M). Maximum sensitivity was observed in March and at the end of August--the beginning of September (KACh in March was equal to 1.27 X X 10(-6) M); at this period of year, ATP content of the hemolymph decreases approximately 100-fold, the release of ATP from the heart in the presence of ACh being also decreased. Maximum level of ATP in cardiac muscle was found in July. It was demonstrated that most significant changes in ACh sensitivity take place during spawning, especially when sex cells are transported from the gonads into the gills, as well as during the release of glochidia from the latter. Possible causes of seasonal changes in ACh sensitivity of cardiac muscle and the role of ATP in this process are discussed.

[Cholinoreception in Ascaris suum (Nematoda) ascarids and the liver fluke Fasciola hepatica (Trematoda)]. / O kholinoretseptsii u askaridy Ascaris sum (Nematoda) i pechenochnoi dvuustki Fasciola hepatica (Trematoda)

Homogenates of synaptically rich structures of the body (the anterior end of A. suum and F. hepatica, as well as narrow strips of the anterior part of A. suum with median nerves and innervation processes of muscle cells) have been tested for the presence of acetylcholine receptor protein (AchR). Strips of the A. suum muscle tissue with low content of synaptic structures served as a control. AchR was detected by the decrease in the optic density at 260 nm and by the decrease in the reactivity of AchR SH-groups in the presence of Ach. Using both methods, AchR was found in water-soluble fraction of tissue homogenates rich in synaptic structures. No AchR was detected in tissues which do not contain synpatic structures. The data obtained are discussed in relation to the function of Ach as a mediator in helminths.

[The role of Ca ions in desensitization induced by acetylcholine]. / Rol' ionov Ca v desensitizatsii vyzvannoi atsetilkholinom

Abolition of cholinergic inhibition in the heart of fresh-water bivalves in absence of cholinesterase can be attained by inactivation of the acetylcholine receptor (R). The role of Ca in this process was studied. Determination of Ca in the perfusate at different stages of cholinergic inhibition showed that the concentration of Ca increased during the sistolic arrest, and the initiation of beats was accompanied by binding of Ca. This coincided with the onset of ATP release and went on till the complete desensitization. The increase of external Ca concentration up to 1.10-2M increased the half-time of desensitization while the binding of Ca with EDTA decreased it and eliminated the ATP anti-acetylcholine effect. Another bivalent ion, UO2, which binds phosphate groups, competes with Ca. The role of Ca and ATP in chemical inactivation of the acetylcholine receptor is discussed.