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The Journal of Neuroscience, May 15, 2002, 22(10):4217-4228

The Effect of Intensity and Duration on the Light-Induced Sodium and Potassium Currents in the Hermissenda Type B Photoreceptor

Kim T. Blackwell

School of Computational Sciences and the Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia 22030

Light duration and intensity influence classical conditioning in Hermissenda through their effects on the light-induced currents. Furthermore, the contribution of voltage-dependent potassium currents to the long-lasting depolarization in type B photoreceptors depends on light-induced currents active at resting potentials. Thus, the present study measures the effect of holding potential, duration, and intensity on the light-induced currents in discontinuous single-electrode voltage clamp mode. Three distinct current components are distinguished by their temporal and voltage characteristics and sensitivity to pharmacological agents. One current component is a transient sodium current, I_Nalgt; another is a plateau sodium current, I_plateau, which persists for the duration of the light stimulus. Substitution of trimethylammonium chloride for sodium reduces both currents equally, suggesting that I_plateau represents partial inactivation of I_Nalgt. The third current component is a prolonged reduction in potassium currents, I_Klgt; it is accompanied by an increase in input resistance, and it appears at potentials close to rest. An increase in light duration or intensity causes an increase in the peak conductance of both I_Nalgt and I_Klgt. Latency of I_Nalgt is decreased by intensity, whereas rise time is increased by duration. An increase in light duration or intensity causes an increase in the time-to-peak and duration of I_Klgt. Characteristics of these currents suggest that I_Klgt is responsible for the long-lasting depolarization seen after light termination, and thus plays a role in classical conditioning.

Key words: associative learning; K⁺ currents; photoreceptors; phototransduction; classical conditioning; leak currents; sodium currents

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Copyright © 2002 Society for Neuroscience  0270-6474/02/22104217-12$05.00/0

This article has been cited by other articles:

				K. T. Blackwell Ionic Currents Underlying Difference in Light Response Between Type A and Type B Photoreceptors J Neurophysiol, May 1, 2006; 95(5): 3060 - 3072. [Abstract] [Full Text] [PDF]

				T. Crow Pavlovian Conditioning of Hermissenda: Current Cellular, Molecular, and Circuit Perspectives Learn. Mem., May 1, 2004; 11(3): 229 - 238. [Abstract] [Full Text] [PDF]

				J. L. Mo and K. T. Blackwell Comparison of Hermissenda Type A and Type B Photoreceptors: Response to Light as a Function of Intensity and Duration J. Neurosci., September 3, 2003; 23(22): 8020 - 8028. [Abstract] [Full Text] [PDF]

				C. T. Tamse, Y. Xu, H. Song, L. Nie, and E. N. Yamoah Protein Kinase A Mediates Voltage-Dependent Facilitation of Ca2+ Current in Presynaptic Hair Cells in Hermissenda crassicornis J Neurophysiol, March 1, 2003; 89(3): 1718 - 1726. [Abstract] [Full Text] [PDF]

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