Amplification vision process

The PC is actually the sum of two processes a fast component, which saturates only at extremely high irradiance levels and a slow component (69). The maximal amplitude amounts only to 10% of the fast component. The fast potential depends solely on the photoconversion rate of the photoreceptor and is the result of a localized calcium influx (67, 68). The late PC is driven by the transport of about 10 elementary charges across the membrane triggered by the absorption of approximately 10 photons. This means there is an amplification of about 10,000 (61). The amplification could be due to the activation of GTP in animal vision one excited rhodopsin can activate up to 500 G proteins, which in turn activate thousands of phosphodiesterase molecules. In Spermatozopsis evidence for the involvement of G-proteins in photoperception was presented (57, 58, 70). Light-dependent GTPase activity in isolated eyespot apparatuses was found with an action spectrum similar to that of rhodopsin absorption. 

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