ELECTROPHYSIOLOGICAL PROPERTIES OF NEWBORN AND ADULT-RAT SPINAL-CORD GLYCINE RECEPTORS EXPRESSED IN XENOPUS-OOCYTES

The properties of glycine receptors (GlyRs) from newborn and adult rat spinal cord were studied in Xenopus oocytes injected with whole mRNA or the heavy (H) or light (L) mRNA fractions encoding their respective GlyRs. Mean open times and conductances of channels gated by H- or L- GlyRs were determined by noise analysis or voltage jumps. We found tha t adult H- and L-GlyRs opened channels that differed in their mean ope n time but had the same channel conductance. Both H- and L-GlyRs gated Cl- currents that displayed a similarly strong outward rectification. Nevertheless, single channels of adult H- and L-GlyRs did not rectify and their mean open times were only slightly altered by voltage. It f ollows that the outward rectification of adult GlyRs is due mainly to a reduction in the number of open channels. In contrast to H-GlyRs, wh ose characteristics seem to remain essentially unchanged with age, L-G lyRs from newborn and adult rats have different properties. Channels o f newborn L-GlyRs have a higher conductance, longer open time, and gre ater voltage dependency than those from the adult. Interestingly, prop erties of newborn GlyRs expressed by whole mRNA were markedly differen t from those encoded by newborn or adult L or H mRNA. These results de monstrate that the functional heterogeneity of GlyRs is developmentall y regulated.