Postnatal DRG neurons express Ca²⁺-permeable and -impermeable kainate receptors. Acutely dissociated DRG neurons expressing kainate receptors were pre-identified by screening for a change in [Ca²⁺]_i in response to 100 μm kainate. Neurons were then voltage clamped at −70 mV using the perforated-patched recording configuration. A, Kainate-induced inward current (bottom trace) is accompanied by a Ca²⁺ increase (top trace) in a P1 DRG neuron, indicating activation of Ca²⁺-permeable kainate receptors. B, Kainate-induced current in a P4 DRG neuron shows an amplitude similar to that of the neuron in A but with no change in [Ca²⁺]_i, indicating the predominant expression of Ca²⁺-impermeable kainate receptors. C, I–V relationship of domoate-induced currents shows a doubly rectifying relation in a P1 DRG neuron different from that shown in A. A voltage ramp (−100 to 100 mV) was introduced before and during the 10 μm domoate application. The two resultingtraces were subtracted to obtain the I–Vcurve as shown. Inset, A high degree of Ca²⁺ permeability determined by simultaneous recording of [Ca²⁺]_i (top trace) and current (bottom trace) from this neuron (n = 5) is shown. The peak amplitudes of the Ca²⁺ response and domoate-induced current are 0.65 and 962 pA. D, A similar experiment in a P7 DRG neuron shows an outwardly rectifying I–V relationship.Inset, The corresponding Ca²⁺permeability is low (n = 3). The peak amplitude of the domoate-induced current is 297 pA. The horizontal bars above each current trace inA–D indicate the duration of drug application.