Proton-induced cation current in embryonic rat spinal cord neurons changes ion dependency over time in vitro

A rapid increase in proton concentration [H+]0 induces Na+ conductance 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 E15 and cultured for up to 14 days revealed that more than 80% had H(+)-induced inward current responses exhibiting a rapid decay phase. The current response was activated beginning about pH 6.8. Following decay, several minutes were required for complete recovery. More modest decreases in pH, which by themselves failed to activate this current, depressed those triggered by effective changes in pH. The currents recorded from cells in culture for less than 7 days could be abolished completely in the absence of Ca2+ and persisted in Na(+)-free and Ba(2+)-containing solutions. Ensemble analysis of current fluctuations recorded at the peak of the current allowed us to estimate a unitary channel conductance of 7.0 pS and a mean open time of 4.1 ms. In neurons cultured 2 weeks or more, protons induced an inward current response with similar kinetic properties, but with [Na+]0 dependency. Thus, proton-activated cation conductance in embryonic rat spinal cord neurons is self-limiting and involves brief openings of cation-selective channels whose ion dependency changes over time in culture.