Increased intracellular sodium mimics some but not all aspects of photoreceptor adaptation in the ventral eye of Limulus.
The effects of the intracellular iontophoretic injection of Na+ ions have been quantitatively compared with adaptation in ventral photoreceptors of Limulus. We find that: (a) both light adaptation and sodium injection are associated with a decrease in the variability of the threshold response amplitued; (b) both light adaptation and sodium injection are associated with a decrease in the absolute value of the temporal dispersion of the threshold response time delay; (c) the same template curve adequately fits the intensity response relationships measured under light adaptation and Na+ injection; (d) both light adaptation and Na+ injection produce a fourfold decrease in response time delay for a desensitization of 3 log units; (e) the time coures of light adaptation and dark adaptation is significantly faster than the onset of and recovery from desensitization produced by Na+ injection; (f) unlike local illumination, Na+ injection does not produce localized desensitization of the photoreceptor. These findings suggest that a rise in intracellular Na+ concentration makes at most only a minor contribution (probably less than 5%) to the total adaptation of these receptors in the intensity range we have examined (up to 3 log units above absolute threshold). However, changes in intracellular Na+ concentration may contribute to certain components of light and dark adaptation in these receptors.
D000200:Action Potentials / Q000187:drug effects; D000221:Adaptation, Ocular; D000818:Animals; D003623:Dark Adaptation; D004558:Electric Stimulation; D006737:Horseshoe Crabs; D066298:In Vitro Techniques; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects; D009799:Ocular Physiological Phenomena; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D013997:Time Factors
D012964:Sodium