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, 2008). Here, we examined single lamprey photoreceptors at the levels of their inner and outer segments using two different recording techniques that provide complementary information, to establish the extent to which SPs operate like jawed vertebrate rods. We found multiple striking similarities that, taken together, argue against convergent evolution, [http://www.selleckchem.com/products/3-deazaneplanocin-a-dznep.html this website] implying that middle Cambrian vertebrates possessed functionally advanced rod precursors. Figure 1. Signal processing in the inner segment of lamprey photoreceptors resembles that found in jawed vertebrates. Results Using Lampetra fluviatilis, collected in Sweden and France during their spawning run, we investigated the function of photoreceptors in retinal slices maintained at a physiological temperature of 9�C11��C. Dark membrane potentials and inner segment properties of SPs and LPs First, we made perforated patch-clamp recordings from photoreceptor inner segments and found that the dark membrane potential was of ?43.2 �� 0.7 mV for SPs (n = 30) and ?45.9 �� 1.1 mV for LPs (n = 10) (Table 1); these values are in line with those of jawed vertebrate rods and cones (Cangiano et al., 2012). Input resistances were 518 �� 41 M? (n = 8; SPs) and 442 �� 68 M? (n = 9; LPs). The membrane time constants, obtained by fitting single exponentials to the early rise of a current step response, were 31.9 �� 4.9 ms (n = 8; SPs) and [http://en.wikipedia.org/wiki/PLK1 Ro3280] 12.9 �� 1.3 ms (n = 9; LPs) (p [http://www.selleckchem.com/products/erastin.html Erastin purchase] LPs (n = 2) expressed the hyperpolarization-activated current Ih, similarly to rods and cones (Della Santina et al., 2012); Ih was abolished by ZD7288 (100 ?M, n = 1 SP; Figure 1B). Table 1. Electrophysiological parameters of SPs and LPs listed in the order they appear in the main text SPs feed their signals to LPs Light stimulation evoked a hyperpolarization in both photoreceptors (Figure 1C,D), with peak changes in membrane potential of up to 30 mV (SPs) and 32 mV (LPs) in response to saturating flashes. The amplitudes of the flash responses from SPs were described by exponential saturation functions (Figure 1C,E). From the curves, we obtained a ratio of 4.4 �� 0.9 (n = 5) for the sensitivities of these photoreceptors at 520 nm and 590 nm. This value is in reasonably good agreement with the ratio of 5.6 predicted by an 11A1 visual pigment template (Govardovskii et al., 2000) having a ��max of 517 nm (Figure 1��figure supplement 1A), the absorbance maximum of SP outer segments found with microspectrophotometry (Govardovskii and Lychakov, 1984), and is thus consistent with the expression of an Rh1 visual pigment.