Temperature transduction in a spider thermosensory cell

Compared to photo-, mechano- and chemoreception, the mechanisms of stimulus transduction and action potential encoding in thermoreceptors are poorly understood. This is mainly because of the small size of thermoreceptive sensory cells, their sparse distribution and the lack of specialized, accessory structures, which have precluded intracellular recordings. Since there are usually several sensory structures located in the vertebrate epidermal skin, there is the problem of identifying the thermosensory cells responsible for action potential recorded. In contrast to the cutaneous thermosensory cells in vertebrates, the superficial thermoreceptive sensilla of arthropods offers the advantage of fairly easy accessibility. While in insects and ticks single warm or cold cells occur together with a pair of hygroreceptors in individual cuticular sensilla, in the spider a group of 7 sensilla each containing a warm cell and a pair of hygroreceptors are combined in a specialized sensory organ, called the tarsal organ. The sense organ is unique to each leg and can be found very readily. We have studied the sense organ extensively both for their structure and function. The problem of how to prepare the spider leg for voltage clamp recordings has been solved recently by scientists in Halifax (Canada) and Frankfurt (Germany) for studying transduction mechanisms on mechanoreceptive sensory cells innervating the slit sense organ of the spider leg. Thus the preparation of the slit sense organ will give way to the preparation of the tarsal organ. The objectives are (1) to obtain for the first time direct electrophysiological analysis of a warm cell by intracellular recording, (2) to investigate how the receptor potential varies with temperature stimulation (i.e., steady temperature, transient and continuous changes in temperature), (3) to test membrane conductance of ions at specific membrane potentials, (4) to measure the ionic currents across the cell membrane that are mediated by specialized channels upon excitation, and (5) to determine how the ion channels are gated.

Compared to photo-, mechano- and chemoreception, the mechanisms of stimulus transduction and action potential encoding in thermoreceptors are poorly understood. This is mainly because of the small size of thermoreceptive sensory cells, their sparse distribution and the lack of specialized, accessory structures, which have precluded intracellular recordings. Since there are usually several sensory structures located in the vertebrate epidermal skin, there is the problem of identifying the thermosensory cells responsible for action potential recorded. In contrast to the cutaneous thermosensory cells in vertebrates, the superficial thermoreceptive sensilla of arthropods offers the advantage of fairly easy accessibility. While in insects and ticks single warm or cold cells occur together with a pair of hygroreceptors in individual cuticular sensilla, in the spider a group of 7 sensilla each containing a warm cell and a pair of hygroreceptors are combined in a specialized sensory organ, called the tarsal organ. The sense organ is unique to each leg and can be found very readily. We have studied the sense organ extensively both for their structure and function. The problem of how to prepare the spider leg for voltage clamp recordings has been solved recently by scientists in Halifax (Canada) and Frankfurt (Germany) for studying transduction mechanisms on mechanoreceptive sensory cells innervating the slit sense organ of the spider leg. Thus the preparation of the slit sense organ will give way to the preparation of the tarsal organ. The objectives are 1. to obtain for the first time direct electrophysiological analysis of a warm cell by intracellular recording, 2. to investigate how the receptor potential varies with temperature stimulation (i.e., steady temperature, transient and continuous changes in temperature), 3. to test membrane conductance of ions at specific membrane potentials, 4. to measure the ionic currents across the cell membrane that are mediated by specialized channels upon excitation, and 5. to determine how the ion channels are gated.