The effects of maintained light stimulation on S-potentials recorded from the retina of a teleost fish.

1. S-potential responses to transient and maintained light stimuli have been recorded from units in the mixed rod-cone retina of a teleost fish species Eugerres plumieri. 2. Four spectral classes of S-potential were observed, three cone- and one rod-type. The cone-type responses were subdivided into two L-type (referred to as L1 and L2), and a C-type response. Two classes of transient depolarization response were also recorded from those retinal levels associated with the S-potential responses and these are attributed, tentatively, to rod and cone bipolar activity. 3. L2-type S-potentials do not yield constant hyperpolarization during maintained light stimulation, the time course of the response potential, V, being given approximately by (see article) where Vt is the response potential at time t sec following the onset of stimulation, Vo being the initial response potential. In contrast, both hyperpolarizing and depolarizing components of the C-type response were maintained under conditions of steady illumination. 4. Under maintained light stimulation at saturation illumination level, the rod S-potentials escape from hyperpolarization in a manner similar to that previously observed for the skate (Dowling & Ripps, 1971). 5. L2-type responses to transient test stimuli of illumination level I, superimposed on a steady background field of illumination level I', are in some respects consistent with Alpern, Rushton & Torii's (1970) empirical formula (see article) with K, I one-half and ID constants. However, for the present data, the value of I one-half is dependent on I'. 6. The significance of Ricco's law for S-potential responses is discussed in relation to these findings.