LANTHANUM BLOCK OF CONTRACTION AND OF RELAXATION IN RESPONSE TO SEROTONIN AND DOPAMINE IN MOLLUSCAN CATCH MUSCLE

  • 1 January 1977
    • journal article
    • research article
    • Vol. 202  (3) , 601-609
Abstract
Contractile and relaxing responses of the anterior byssus retractor muscle of Mytilus edulis L. were observed after exposure to La3+. After 25 min in 5 mM La3+, contraction in response to acetylcholine, to KCl and to stimulation of i.m. nerves is blocked, whereas contraction in response to direct current pulses is partially blocked and caffeine contraction is unaffected. Exposure to 5 mM La3+ for 3 h does not block relaxation of catch tension in response to serotonin and dopamine but exposure to 5 mM La3+ in the presence of a depolarizing agent (acetylcholine or KCl) for a brief period (4 min) abolishes the relaxing response. Activation of contraction in the anterior byssus retractor muscle can be effected by Ca2+ influx from the bathing medium and/or by release of Ca2+ from internal sites, depending on the nature of the stimulation. The relaxing action of serotonin and dopamine depends neither on Ca2+ influx nor on passive efflux of Ca2+, but rather on Ca2+ combining at an internal site or at sites on the cell membrane which are exposed when the muscle is depolarized.

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