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Photoreceptors in primitive chordates: fine structure, hyperpolarizing receptor potentials, and evolution
Science (New York, N.Y.)
|June 4, 1971
Summary
Primitive chordates exhibit light responses similar to vertebrates. However, the structure of their light-sensing cells does not correlate with the type of response observed.
Area of Science:
- Comparative physiology
- Cell biology
- Evolution of vision
Background:
- Vertebrates possess hyperpolarizing photoreceptor potentials.
- Primitive chordates offer insights into the evolution of visual systems.
Purpose of the Study:
- To investigate the photoreceptor potentials in primitive chordates.
- To compare the fine structure of photoreceptive membranes in different species.
- To determine if there is a functional correlation between membrane structure and response polarity.
Main Methods:
- Electrophysiological recording of photoreceptor potentials.
- Electron microscopy of photoreceptive membranes.
Main Results:
- Two species of primitive chordates, Salpa and Amaroucium, exhibit hyperpolarizing photoreceptor potentials, similar to vertebrates.
- In Salpa, the photoreceptive membrane is composed of microvilli.
- In Amaroucium, the photoreceptive membrane is modified from cilia.
Conclusions:
- The presence of hyperpolarizing photoreceptor potentials is conserved in some primitive chordates.
- Photoreceptive membrane structure (microvilli vs. cilia) does not appear to dictate the polarity of the light response.
- This suggests a divergence between structural organization and functional response in the evolution of photoreception.
