Fig. 5. Insulin-like growth factor I (IGF-I) increases the cyclic-nucleotide-sensitivity of rod cyclic-nucleotide-gated (CNG) channels. (A) An increase in amplitude of the currents activated by application of 8-Br-cGMP (1, 2.5, 10, 25 and 250µmoll^-1 from left to right) in excised patches from rods exposed to control saline or to saline containing 10µmoll^-1 IGF-I for 10min prior to patch excision. (B) Effects of a 10min pretreatment with 1nmoll^-1 to 100µmoll^-1 IGF-I (values are means + S.E.M., N=7–25) on the apparent affinity of CNG channels. (C) A suction pipette was used to record the light response of the rods via the inner segment (IS) while permitting continuous superfusion of control or IGF-I-containing solutions on the outer segment (OS). (D) Average rod photoresponse waveforms in response to dim and saturating 10ms light flashes (at time zero) recorded in control saline and 4–6min after the beginning superfusion with 1µmoll^-1 IGF-I.