| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [MembBiophys] |
In addition to regular photoreceptors, some invertebrates possess simple extra ocular photoreceptors. For example, the central ganglia of molluscs contain photosensitive neurons. These neurons are located on the dorsal surface of the ganglia and based on their electrophysiological properties, it has been postulated that they the internal photoreceptors. However, besides the eye, transduction of the light also occurs in these extra-ocular photoreceptors. In the present work we analyse the reactivity of these nerve cells to light and describe the underlying mechanism mediating the light-induced response. The experiments were carried out on the isolated subesophageal ganglionic complex of Helix pomatia. The effect of light was tested by illuminating the cell for 10-20 sec followed by 1 min darkness. Identified photosensitive neurons in the left parietal ganglion were impelled by a single K-citrate filled microelectrode. A single voltage-clamp apparatus was used for current and voltage measurements. The tested photosensitive cell reacted to illumination with depolarization and increment of frequncy of spontaneously generated action potential. In identified photosensitive neuron the onset of light prolongs significantly (by about 40%) the duration of the action potential. The onset of light induced constantly an enhancement of calcium inward current. The prolongation of the action potential was time and temperature dependent suggesting involvement of some second messenger in the light-induced modulation of voltage-gated channels. Experiments studying the photosensitive neurons can not only provide the understanding of the behavioral significance of the photoexcitative neurons, but they also allow the comparative study of the physiological mechanisms involved in the photo transduction of the simple photo sensory systems.
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