title: Light response of a giant Aplysia neuron.
abstract: 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 E(K) 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 E(K). 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 Ca(2+) into this neuron also hyperpolarizes the cell membrane. This effect is also due largely to an increase in K(+) conductance. The light response after Ca(2+) 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 Ca(2+) which in turn increases K(+) conductance, thereby hyperpolarizing the neuronal membrane.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D005724:Ganglia / Q000502:physiology; D008027:Light; D008564:Membrane Potentials; D008974:Mollusca / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium; D002118:Calcium