Ionic currents in cultured dorsal root ganglion cells from adult guinea pigs

Abstract

Ionic currents in cultured dorsal root ganglion (DRG) neurons fromadult guinea pigs were analyzed by voltage-clamp techniques. The Na⁺ inward current had a reversal potential at +33mV, and revealed activation and inactivation kinetics similar to those of squid giant axons. A typical value for the maximum Na⁺ conductance was 178 mS/cm² and the peak current was 2.5mA/cm². The delayed K⁺ outward current showed a fast and a slow phase of inactivation and was sensitive to tetraethylammonium (TEA; ∼130mm) and 4-aminopyridine (∼2mm). The maximum K⁺ conductance was 26±9 (mean±sd) mS/cm². The slow Ca²⁺ inward current was identified in Na⁺-free, TEA-containing solution. Its peak value was increased by 1.7-fold when [Ca²⁺]_o was increased from 5 to 10mm. The current was blocked by Co²⁺ but not by tetrodotoxin. Sr²⁺ and Ba²⁺ could substitute in carrying this current. The maximum peak of the Ca²⁺ current was 0.22±0.14mA/cm². At potentials positive to 0mV, the Ca²⁺ current was often followed by a slowly developing outward current, which was also sensitive to Co²⁺, suggesting a Ca²⁺-activated outward current. It is concluded that the action potential of theadult guinea pig DRG neuron is mediated by Ca²⁺ as well as by Na⁺ and K⁺ currents. The current densities of these ionic channels are considered to be different fromembryonic neurons and from nodes of Ranvier.