PROTON-INDUCED CATION CURRENT IN EMBRYONIC RAT SPINAL-CORD NEURONS CHANGES ION DEPENDENCY OVER TIME IN-VITRO

A rapid increase in proton concentration [H+](o) induces Na+ conductan ce in a variety of cell types. Here we report that H+ trigger a cation -selective channel whose ion dependency changes over time in culture. Whole-cell recordings of ventral spinal cord neurons dissociated at E1 5 and cultured for up to 14 days revealed that more than 80% had H+-in duced inward current responses exhibiting a rapid decay phase. The cur rent response was activated beginning about pH 6.8. Following decay, s everal minutes were required for complete recovery. More modest decrea ses in pH, which by themselves failed to activate this current, depres sed those triggered by effective changes in pH. The currents recorded from cells in culture for less than 7 days could be abolished complete ly in the absence of Ca2+ and persisted in Na+-free and Ba2+-containin g solutions. Ensemble analysis of current fluctuations recorded at the peak of the current allowed us to estimate a unitary channel conducta nce of 7.0 pS and a mean open time of 4.1 ms. In neurons cultured 2 we eks or more, protons induced an inward current response with similar k inetic properties, but with [Na+](o) dependency. Thus, proton-activate d cation conductance in embryonic rat spinal cord neurons is self-limi ting and involves brief openings of cation-selective channels whose io n dependency changes over time in culture. (C) 1997 Elsevier Science B .V.