| Comments |
“There are two primary components of the cellular
dark noise, each of which contributes about equally to the total variance of the dark current (Baylor, Matthews, and Yau, 1980). One component consists of occasional discrete events that resemble single-photon responses [arrows in Fig. 6(a)]. These events originate
from thermal isomerization of rhodopsin and occur
about once every 30 sec in a toad rod at 20°C (Baylor, Matthews, and Yau, 1980) and about once every 90 sec in a mammalian rod at 37°C (Baylor, Nunn, and Schnapf, 1984). The toad rod contains about 3×10^9 rhodopsin molecules, so each rhodopsin activates spontaneously only once every few thousand years-the mammalian rod contains about 10^8 rhodopsins, each of which activates spontaneously about once every 300 years at 37°C.” |