Appearance and maturation of voltage-dependent conductances in solitary spiking cells during retinal regeneration in the adult newt.

Electrical membrane properties of solitary spiking cells during newt (Cynops pyrrhogaster) retinal regeneration were studied with whole-cell patch-clamp methods in comparison with those in the normal retina. The membrane currents of normal spiking cells consisted of 5 components: inward Na+ and Ca++ currents and 3 outward K+ currents of tetraethylammonium (TEA)-sensitive, 4-aminopyridine (4-AP)-sensitive, and Ca(++)-activated varieties. The resting potential was about -40 mV. The activation voltage for Na+ and Ca++ currents was about -30 and -17 mV, respectively. The maximum Na+ and Ca++ currents were about 1057 and 179 pA, respectively. In regenerating retinae after 19-20 days of surgery, solitary cells with depigmented cytoplasm showed slow-rising action potentials of long duration. The ionic dependence of this activity displayed two voltage-dependent components: slow inward Na+ and TEA-sensitive outward K+ currents. The maximum inward current (about 156 pA) was much smaller than that of the control. There was no indication of an inward Ca++ current. During subsequent regeneration, the inward Ca++ current appeared in most spiking cells, and the magnitude of the inward Na+, Ca++, and outward K+ currents all increased. By 30 days of regeneration, the electrical activities of spiking cells became identical to those in the normal retina. No significant difference in the resting potential and the activation voltage for Na+ and Ca++ currents was found during the regenerating period examined.