Fig. 1. The Ligia heart and the experimental setup. (A) Dorsal view of Ligia exotica showing the location of the tubular heart. The dorsal carapaces were partly removed to view the heart. (B) A schematic drawing of an opened heart viewed from the ventral side. CGN, cardiac ganglion neuron; HM, heart muscle; O, ostium. (C) A schematic drawing of the experimental setup for transversely stretching an opened heart. FS, fixed stage; HM, heart muscle; M, microelectrode; PS, pericardial septum; T, tergite; US, unfixed stage. After dissection (see Materials and methods), the lateral rims of the tergites remained attached to the heart via pericardial septum. The tergites were pinned on two separate Sylgard stages. One stage was pinned onto the bottom of the experimental chamber and the other stage was connected to a servomotor via a steel wire. By displacing the unfixed stage (arrow), one can apply stretch to the heart muscle. The ganglionic bursting activity was monitored by recording the CG-evoked excitatory junctional potentials (EJPs) intracellularly from the heart muscle. The inset shows a single burst of two EJPs recorded from the ostial muscle (calibration: 20 mV, 0.1 s).

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