Figure 4.

Expression of light-activated channels confers light sensitivity on hippocampal pyramidal neurons. (a) Spontaneous action potentials are silenced and revived by exposure to 390- and 500-nm light, respectively. A neuron that was transfected with the multiply mutated Shaker channel was treated for 15 min with MAL-AZO-QA before recording. The frequency of spontaneous synaptic potentials generated by untransfected presynaptic neurons is not affected by light. (b) Depolarizing current steps elicit repetitive firing in 500-nm light (left) but only single action potentials in 390-nm light (right). Neurons were held under current clamp at about −55 mV and were depolarized to about −15 mV. (c) Summary of repetitive firing data. Number of spikes resulting from a suprathreshold depolarization to −15 mV is significantly modulated by light in the multiply mutated Shaker-transfected neurons treated with MAL-AZO-QA (*P < 0.01). Neurons expressing the channel without MAL-AZO-QA treatment or treated with MAL-AZO-QA without channel expression were unaffected by light.