Ca2+ is an obligatory intermediate in the excitation cascade of limulus photoreceptors.
We have investigated the role of Ca2+ in the excitation of Limulus photoreceptors by intracellular injection of the Ca2+ buffer, 5,5'-dibromo-BAPTA. Buffer with free Ca2+ of 0.5 or 5 microM slowed the rising edge of the light response over 100-fold and greatly reduced both the transient and plateau phases of the light response, as expected if Ca2+ elevation is necessary for all phases of excitation. Injection of buffers with free Ca2+ of 5 or 45 microM, levels normally reached during light, evoked sustained inward current as expected if Ca2+ is sufficient for excitation. The transduction cascade appears due to a single pathway that sequentially involves 1,4,5-trisphosphate inositol, Ca2+, and cyclic GMP.[1]References
- Ca2+ is an obligatory intermediate in the excitation cascade of limulus photoreceptors. Shin, J., Richard, E.A., Lisman, J.E. Neuron (1993) [Pubmed]
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