Reduction of glial proliferation by K+ channel blockers is mediated by changes in pHi

Astrocyte proliferation was studied in primary cultures of rat spinal cord by [3H]thymidine uptake and was significantly reduced by culturing cells for 24 h in the presence of agents known to block astrocytic K+ channels: Cs+, Ba2+, 4-AP and tetraethylammonium (TEA). To determine whether effects were mediated by changes in Vm or pHi, these parameters were studied electrophysiologically or ratiometrically, using BCECF. Of the four K+ channel blockers, only Ba2+ depolarized astrocytes significantly. However, all four K+ channel blockers resulted in an alkaline shift in pHi. Under culture conditions that altered pHi in a defined way, proliferation strongly depended on pHi, with highest rates at pH approximately 6.7 and growth inhibition at more acidic or alkaline conditions. These observations suggest that astrocyte proliferation is sensitive to changes in pHi and that K+ channel blockers may exhibit their antiproliferative effects through changes in pHi.