Involvement of calcium-activated potassium channels in the regulation of DNA synthesis in cultured Muller glial cells

PURPOSE. TO determine the involvement of Ga2+-activated K+ channels of big conductance (BK) and of Ca2+ channels in the regulation of DNA synthesis in cultured guinea pig Muller cells. DNA synthesis was stimulated by elevated extracellular potassium, by serum, or by epidermal growth factor. METHODS. Dissociated retinas from guinea pigs were cultured for 8 days. Jus t before confluence was achieved, the cultures were treated with the test s ubstances in serum-free or serum-containing media. The rates of DNA synthes is were assessed by a quantitative bromodeoxguridine immunoassay. The intra cellular Ca2+ concentration was measured by the fura-2 fluorescence techniq ue. RESULTS. Blocking the BK channels with tetraethylammonium or by iberiotoxin had no effect at normal extracellular K+ (5.8 mM) but decreased the rate o f DNA synthesis at higher extracellular K+ (10 or 25 mM). Epidermal growth factor-induced DNA synthesis was decreased by block of BK channels or by ap plication of the Ca2+ channel blockers nimodipine and flunarizine. Applicat ion of epidermal growth factor elevated the intracellular Ca2+ concentratio n of cultured Muller cells. This elevation was diminished by co-application of iberiotoxin or of flunarizine. CONCLUSIONS. The activity of BK channels is necessary for elevated DNA synt hesis in Muller cells when their membranes are depolarized and/or when the Ca2+ influx into Muller cells is increased by growth factors. BK channels m ay contribute to the maintenance of DNA synthesis by increasing mitogen-ind uced increase in intracellular Ca2+ concentration.