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The Journal of General Physiology, Vol 62, 239-254, Copyright © 1973 by The Rockefeller University Press

ARTICLE

Light Response of a Giant Aplysia Neuron

Arthur M. Brown 1 and H. Mack Brown 1

1 From the Departments of Physiology and Medicine, College of Medicine, University of Utah, Salt Lake City, Utah 84112.

A. M. Brown's present address is the University of Texas Medical Branch, Galveston, Texas 77550.

Illumination of an Aplysia giant neuron evokes a membrane hyperpolarization which is associated with a membrane conductance increase of 15%. The light response is best elicited at 490 nM: the neuron also has an absorption peak at this wavelength. At the resting potential (-50 to -60 mV) illumination evokes an outward current in a voltage-clamped cell. This current reverses sign very close to EK calculated from direct measurements of internal and external K+ activity. Increases in external K+ concentration shift the reversal potential of the light-evoked response by the same amount as the change in EK. Decreases in external Na+ or Cl- do not affect the response. Therefore, the response is attributed to an increase in K+ conductance. Pressure injection of Ca2+ into this neuron also hyperpolarizes the cell membrane. This effect is also due largely to an increase in K+ conductance. The light response after Ca2+ injection does not appear to be altered. Pressure injection of EGTA abolished or greatly reduced the light response. The effect was reversible. We suggest that light acts upon a single pigment in this neuron, releasing Ca2+ which in turn increases K+ conductance, thereby hyperpolarizing the neuronal membrane.

Submitted on March 30, 1973


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