Measuring Tension Development and Membrane Response in Muscle Fibers of the Crayfish Heart

    The crustacean heart is a single-chambered sac composed of layers of myocardial fibers. The heart contains ostial and cardio-arterial valves with muscular leaflets. During cardiac pumping, blood from the pericardial cavity enters the heart through the ostia and is pumped out to the arteries through the cardio-arterial valves. I examined the electrical and contractile properties of these muscles in the heart of the decapod, Procambarus clarkii, and their responses to pericardial organ (PO) neurohormones.
 

experimental arrangement

    The muscle specimen was pinned on the silgard block in deep experimental chamber. Fresh crayfish saline containing 0.1-1 microM TTX was continuously applied onto the specimen.
    TTX stops the spontaneous heart beat by blocking voltage-gated Na channel in the cardiac ganglion neurons (cardiac pacemaker).
    In some experiments, saline containing TTX and various pericardial organ neurohormons (Oct, 5-HT, Dop, Proc., etc.) was applied to examine their modulatory effects onto the muscle fibers.
 

recordings of membrane and contractile responses of the muscle fibers to injected current pulse

    Simultaneous recordings of the membrane potential and the isometric tension of the muscle were performed using glass capilary microelectrodes and a strain guage mechano-electric transducer.  The muscle fiber was stimulated by injecting square current pulses through another microelectrode.
    Vm: membrane poetential.

Back...