Voltage dependent ion channels in transduction and adaptation in the stretch receptor neurons of the crayfish

	Voltage dependent ion channels in transduction and adaptation in the stretch receptor neurons of the crayfish
Research field:	Central nervous system
Authors:	Rydqvist B, Swerup C, Lin J-H, Sand P
Address of presenting author:	Dept Physiology & Pharmacology, Karolinska Institutet, S-171 77 Stockholm
E-mail:	Bo.Rydqvist@fyfa.ki.se
Phone:	+468-7287267
Fax:	+468-327026
Text of abstract	Introduction The crayfish stretch receptor organ, an analogue to the human muscle spindle is a good model for the analysis of different aspects of mechanotransduction. Previous results from the stretch receptor neurons of the crayfish have demonstrated that both the viscoelastic properties of the receptor muscles, the mechanosensitive ion channels generating the receptor current, and the K⁺ and Na⁺ permeabilities and the passive membrane properties all contribute to the difference in impulse generation and adaptation seen in the two recepor organs (Swerup & Rydqvist 1992). However, it is not clear to what extent, and how, voltage gated ion channels contribute to the difference in adaptation between the slowly and rapidly adapting neuron. In this study we have analysed how voltage gated ion channel kinetics and spatial distribution can influence the functional properties of sensory neurons. Methods The experiments were carried out on the isolated slowly and rapidly adapting stretch receptors of the crayfish using intracellular two microelectrode voltage clamp technique or the patch clamp technique. The intracellular electrodes were pulled to a tip diameter of 0.2 to 0.5 um and filled with 3 M KCl (2-5 MO). Patch clamp was performed using an Axoclamp 200A amplifier with large tip electrodes (3 - 12 um) for macropatch application, or small tip electrodes (2 um) for single channel recordings, filled with normal saline. Mathematical modeling of the neuron was made using a conventional Hodgkin-Huxley model. Results The kinetics of the Na⁺ and K⁺ channels were defined from patch-clamp experiments using macropatches. In this way normal parameters for activation and inactivation could be obtained. Manipulating the activation and inactivation parameters of the Na⁺ channels showed that both processes can, with small changes, affect the adaptive behaviour of the neuron when stimulated electrically. Small changes in the inactivation parameters was less effective as compared to changes in the activation parameters. When both activation and inactivation were changed profound alterations of the neuron behaviour were observed. Conclusions In the present study, computation of the impulse response to electrical stimulation of the neuron showed that small changes of activation and/or inactivation parameters can dramatically affect the adaptive behaviour of the neuron. The differences in parameters were in the same range as those experimentally obtained between the slowly and rapidly adapting neurons. References Swerup C. & Rydqvist B. 1992. Comp Biochem Physiol 103A,423-431
Keywords:	crayfish, stretch receptor, mechanoreceptor, adaptation, model

Created 2000-05-03