大蛤조개의 心運動에 關한 硏究

Abstract

[한글]

[영문]

Although two kinds of fibers in the cardioregulator nerves of Venus have not been distinguished histlogically, it has been postulated that they may be composed of both inhibitory and excitatory fibers (Carlson, 1905). Prosser (1940), Welsh and Slocombo (1952) reported that stimulation of the cardioregulator nerves of molluscs caused an caridac inhibition by releasing acetylcholine. However, the chomical nature of the augmentory substance in the heart was obacure until Erspamer and Ghiretti (1955) found that onteramine, which has been known as 5-hydroxytryptamine (5-HT), has an oxcitatory action on the hearts of the molluscs. 5-HT has been demonstrated to be normally present in the heart of molluscs and to be the excitatory mediator in the heart (Welsh & Moorhead, 1959b). The present study was undertaken in an attompt to clearify the nature of the acetylcholine receptor and 5-HT receptor in the heart of Mecretrix Lamacki.

Materials and Methods

Large, fresh Meretrix Lamacki used in this study were obtained from the market and maintained in a refrigerator at r℃ for various periods of time which did not exceed one week. The ventricle of Meretrix Lamacki was excised ans suspended in a

muscle chamber conaining 100 ml of artificial soa-water at a constant temperature of 25℃. Air was bubble through the bathing fluid.

The isatonic comtractile amplitude and the rate of spentaneous boat were recarded on a smoked drum. The magnitude of change in contractile amplitude was expressed as a percentage change relative to the amplitude recorded just prier to the addition

of the drug.

Results and Conclusion

1. 5-Hydroxytryptamine exerted a constant and marked excitatory effect on the isalated molluscan heart. The excitatory response to 5-HT was more pronounced in the summer than in the winter.

Pretreatment with atropine, concaines or morphine has little effect, if any, on the excitatory response to 5-HT of the isolated molluscan heart. On the other hand, dibonamins markedly depressed, and 2-bromolysergic acid diethyalmide (BOL-148) or

methysergide almost completely blocked the excitatory activity of 5-HT on the melluscan heart. Gaddum and Picarelli (1957) reported that there are two types of 5-HT receptors, namely the N-receptor and D-receptor; the former is blocked by morphine or atropine; the latter blocked by dibenzyline or LSD. On the basis of this classification of 5-HT receptors, the receptor in the molluscan heart appears to have a nature which is closely rolated to the D-receptro.

2. Acetylcholine exhibited a marked inhibitory effect on the isolated molluscan heart. The effect was more pronounced in winter than in summer.

The pretroeatmont with stropine failod to block the inhibitory activity of acotylcholine indicating that the acotylcholine receptor in the mulluscan hoart differs from that in the mammalinan heart. A large dose of nicotine markedly blocked the action of actoylcholine but heamotheniur had no effect. This result is not compatible with the view that the molluscan heart is pharmacologically similar to autoneric ganglic. d-Tubocurarine depressed but did not completely block the activity of acotylcholine, while benzoquinoniur completely and spocifically blocked the inhibtar action of acetylcholino. The above rosults indicate that the cetylcholine receptor in the molluscan heart has a peculiar nature which is different from that described for the mammalian tissue.