Fig. 6. Cytoplasmic free Ca²⁺ concentrations in individual rod cells measured before, during and after exposure to light (A; N=16), quinpirole (B; N=17) or 8-pCPT-cGMP and dopamine treatment (C; N=17). (A,B) Light or quinpirole treatment decreased cytoplasmic Ca²⁺ concentrations. Horizontal lines represent the duration of light or drug treatment. (C) The application of 8-pCPT-cGMP (a membrane-permeable cGMP analog) increased Ca²⁺ influx. However, when dopamine was added to the medium, cytoplasmic Ca²⁺ concentrations decreased. Horizontal solid and broken lines represent 8-pCPT-cGMP and dopamine treatments, respectively. Each line represents time-lapse imaging data from one rod cell. (D) Decreases in cytoplasmic Ca²⁺ concentrations after 8-pCPT-cGMP and dopamine treatments in the absence (N=17; open bar) or presence of Co²⁺ (N=8; hatched bar). Values are the means ± s.e.m.; ns, no significant difference.