RECIPROCAL EXPRESSION OF CELL-CELL COUPLING AND VOLTAGE-DEPENDENT NA CURRENT DURING EMBRYOGENESIS OF RAT TELENCEPHALON

Using whole-cell patch-clamp techniques in situ (whole-tissue and tiss ue slices), we have studied two aspects of rat telencephalic cell deve lopment during the period of embryogenesis starting at E12. The first aspect was related to junctional coupling as revealed by low input res istance, intercellular dye spread and pharmacologic blockade. Coupling appeared to decrease with time, both in extent and occurrence. The se cond aspect dealt with cell excitability as revealed by voltage-depend ent Na current (I(Na)) expression. Immature action potentials and thei r underlying I(Na)s were present in a small proportion of E12 cells. T hese currents were blocked 36% and 78% by 10(-7) M and 10(-6) M tetrod otoxin (TTX), respectively. From then onward, IN.s got larger and more prevalent while no obvious changes in kinetics were observed. At E21, I(Na)s were abolished by 10(-7) M TTX and channel density apparently was sufficient to support overshooting yet still immature action poten tials.