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1. Electrical properties of the membrane of photoreceptor cells in the lateral ocelli of barnacles, Balanus amphitrite and B. eburneus were investigated by intracellular recording, polarization and voltage-clamp techniques.

2. The resting potential of a dark adapted cell was 36·3 ± 6·6 mV (S.D.) and depended mainly on the external K⁺ concentration.

3. Current—voltage relations obtained from voltage—clamp experiments in the absence of light were non-linear and varied with time after the onset of a step change in membrane potential; the steady state was reached after about 0·5 sec.

4. Illumination resulted in a membrane potential change under current clamp and in a change of membrane current (light-initiated membrane current (L.I.C.): total membrane current with illumination minus current without illumination) under voltage—clamp conditions. Amplitudes and time course of L.I.C. depended on the light intensity as well as membrane potential.

5. The L.I.C.-voltage relation was non-linear and corresponded with a slope conductance increase with increasing positive membrane potential.

6. The reversal potential of L.I.C. was independent of the light intensity and the time after onset of illumination; the average value obtained in normal saline was +26·9 ± 5·0 mV.

7. The membrane conductance estimated from instantaneous L.I.C.-voltage relations agreed with the chord conductance of the non-linear L.I.C.-voltage relation.

8. Decreasing external Na⁺ concentration decreased the inward component of L.I.C. but not the outward component.

9. Decreasing external Ca²⁺ concentration increased the inward as well as the outward component of L.I.C.

10. The reversal potential shifted in the negative direction with decreasing external Na⁺ concentration (the rate was 10-15 mV for a tenfold change in concentration) and the rate was augmented in the absence of Ca²⁺ but did not exceed 21 mV.

11. The change of reversal potential with changes of external Ca²⁺ concentration was negligible in normal Na⁺ media but was significant in the absence of Na⁺ (rate as high as 20 mV).

12. Alteration of the external K⁺ or Cl^- concentrations did not affect the amplitude or reversal potential of L.I.C.

13. The results indicate that illumination increases the membrane permeability mainly to Na⁺ ions and that the primary effect of Ca²⁺ ions is suppression of the permeability increase; Ca²⁺ permeability may increase slightly during illumination.

This article has been cited by other articles:

				S. Ozawa, S. Hagiwara, K. Nicolaysen, and A. E. Stuart Signal Transmission from Photoreceptors to Ganglion Cells in the Visual System of the Giant Barnacle Cold Spring Harb Symp Quant Biol, January 1, 1976; 40(0): 563 - 570. [Abstract] [PDF]