Figure 1. [Ca²⁺]_i baseline in light adapted rods is sustained by tonic Ca²⁺ influx.

A, Ca²⁺ removal from the saline solution results in decrease in [Ca²⁺]_i. B, [Ca²⁺]_i follows changes in the driving force for Ca²⁺ entry as [Ca²⁺]_o is increased from 1 to 10 mm (C). 1 μm Gd³⁺ or La³⁺ decrease baseline [Ca²⁺]_i, whereas agonist (FPL 64176) and antagonists (nifedipine and Cd²⁺) of L-type voltage-operated Ca²⁺ channels have no significant effect on [Ca²⁺]_i baseline. D, FPL 64176 augmented [Ca²⁺]_i elevation evoked by 30 mm KCl.