Rectification of the photocurrent. (A and B) The nonlinear conduction of the photocurrent is not an artifact of intracellular perfusion. A Hesse cell was whole cell clamped with the perforated-patch technique using nystatin. After access resistance attained a stable level, the protocol of light stimulation (7.2 × 10¹³ photons/cm²) and membrane depolarization was applied. The resulting light-evoked currents rectified in the inward direction like in control conditions. (C and D) Rectification is not a result of voltage-dependent block by intracellular magnesium ions. Similar experiments were performed with an intracellular solution in which Mg was omitted. The inward rectification was unaffected. Flash intensity: 3.8 × 10¹² photons/cm²).