COMPARATIVE-ANALYSIS OF IONIC CURRENTS IN THE SOMATIC MEMBRANE OF EMBRYONIC AND NEWBORN RAT SENSORY NEURONS

Inward currents in the somatic membrane of dissociated rat dorsal root ganglion neurons have been studied in two groups of animals (17 days of embryonic development and the first day after birth) by suction pip ette (whole-cell configuration) and voltage-clamp techniques. Altogeth er 157 neurons were examined. Four components in the inward currents h ave been identified: fast tetrodotoxin-sensitive (I-Na(f)) and slow te trodotoxin insensitive (I-Na(s)) sodium, low-(I-Ca(l)) and high-thresh old (I-Ca(h)) calcium currents. The percentage of neurons demonstratin g four types of inward currents I-Na(f), I-Na(s), I-Ca(l), I-Ca(h) inc reased from 21% in embryo to 61% in newborn. The percentage of neurons with I-Na(f), I-Na(s) and I-Ca(h) increased from 4% in embryonic to 1 4% in the first day after birth. The percentage of cells with I-Na(f) I-Ca(f) and I-Ca(h) (without tetrodotoxin-insensitive I-Na(s)) decreas ed from 56 to 11% in embryo and newborn rats, respectively. A statisti cally significant linear correlation was found between the densities o f I-Na(f), and I-Ca(h) currents for both ages. A correlation also occu rred between the densities of I-Na(s) and I-Ca(h),. A reciprocal relat ion between the densities of both types of calcium currents and the si ze of cell soma was found in the neurons with all four types of inward currents from newborn animals. A comparison of these data with previo us study of inward currents during postnatal development indicates tha t the most dramatic changes in their distributions and mean densities takes place some time after the birth of the animals.