Effect of Low Extracellular Calcium Concentration on Photosensitivity of Isolated Rods From Frog Retina Available to Purchase

The effects of extracellular calcium concentration ([Ca²⁺]_o) on the light sensitivity of isolated single rods from the retina of the frog (Rana catesbeiana) were investigated by sucking the rod inner segments into tightly fitting pipettes.

Light flashes (500nm, 1 s duration) evoked transient outward changes of membrane current (photoresponses). The peak amplitude of maximal photoresponses in normal physiological solution varied between 6 and 12 pA. Reducing [Ca²⁺]_o from 0·9 mmol l⁻¹ (normal Ca²⁺) to 90 μmol l⁻¹ (low Ca²⁺) increased the peak amplitude of photoresponses and shortened the recovery phase of the responses.

The effects of larger changes in light intensity were also investigated. After light-on there was a steady outward change of membrane current, and after light-off the current recovered to the initial dark level. With a low external Ca²⁺ concentration, light-off induced a large inward change of membrane current which transiently overshot the initial dark level. During the overshoot stage, light flashes evoked photoresponses which were larger than those in the initial dark period.