Figure 2.

Intrinsic photosensitivity of iris sphincter muscle of other mammals. 35–37°C. a, Flash intensity-response relations from robust light responses of albino rat and pigmented hamster muscles (2 for rat and 3 for hamster). Same fits as in Fig. 1, with I₀ (averaged across individual muscles) being 4.3×10⁷ photons μm⁻² and 4.6×10⁷ photons μm⁻² (436 nm) for rat and hamster, respectively. Flashes were 12–400 ms. Insets show sample responses from a muscle of each species to dim and saturating flashes. 3.4×10⁶ and 2.1×10⁸ photons μm⁻² for rat and 1.6×10⁶ and 3.6×10⁸ photons μm⁻² for hamster, respectively (436-nm Hg light). b, Similar experiments on dog (representative of 2 muscles), rabbit (3), cat (1) and rhesus monkey (7). All steps and the flash (600-ms) delivered 6.1×10⁹ photons μm⁻² s⁻¹ (436-nm). Monkey muscle (pre-incubated with 30-μM 9-cis-retinal for 1 hr) gave no obvious light response, but responded to 50-μM acetylcholine in bath (black bars). Fast deflections in the rabbit and cat experiments reflected spontaneous muscle contractions/relaxations of unknown cause. 5-mm-diameter light spot, covering entire muscle of rat, hamster, cat and rabbit, but only partially the larger muscles of others.