Rod photoresponses in the absence of external sodium in retinae treated with phosphodiesterase inhibitors.

Exposure of isolated toad retinae to phosphodiesterase inhibitors induced changes in the ionic permeability of rod cells. Under similar conditions intracellularly recorded light responses were observed also in the absence of external Na+. Hyperpolarizing photoresponses in Na+-free media required the presence of divalent cations among which Mg2+, Mn2+ and Ba2+ were the most effective.