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Figure 5 | BMC Neuroscience

Figure 5

From: The excitation cascade of Limulus ventral photoreceptors: guanylate cyclase as the link between InsP3-mediated Ca2+release and the opening of cGMP-gated channels

Figure 5

A model for Limulus excitation. The cascade is initiated by the isomerization of rhodopsin to metarhodopsin by light. Metarhodopsin catalyzes exchange of GTP for GDP on multiple G proteins (Gq). Gq-GTP binds and activates phospholipase C (PLC). This complex cleaves phosphatidyl inositol-4,5-bisphosphate (PIP2) producing InsP3. InsP3 opens Ca2+ ion channels in the endoplasmic reticulum (ER) leading to the release of Ca2+ into the cytosol. Ca2+ release activates GC. A rise in cGMP opens cyclic nucleotide-gated ion channels (CNCG) in the plasma membrane.

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