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

PURPOSE: To determine the involvement of Ca(2+)-activated K(+) channels of big conductance (BK) and of Ca(2+) channels in the regulation of DNA synthesis in cultured guinea pig Müller 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. Just before confluence was achieved, the cultures were treated with the test substances in serum-free or serum-containing media. The rates of DNA synthesis were assessed by a quantitative bromodeoxyuridine immunoassay. The intracellular Ca(2+) concentration was measured by the fura-2 fluorescence technique. RESULTS: Blocking the BK channels with tetraethylammonium or by iberiotoxin had no effect at normal extracellular K(+) (5.8 mM) but decreased the rate of 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 application of the Ca(2+) channel blockers nimodipine and flunarizine. Application of epidermal growth factor elevated the intracellular Ca(2+) concentration of cultured Müller cells. This elevation was diminished by co-application of iberiotoxin or of flunarizine. CONCLUSIONS: The activity of BK channels is necessary for elevated DNA synthesis in Müller cells when their membranes are depolarized and/or when the Ca(2+) influx into Müller cells is increased by growth factors. BK channels may contribute to the maintenance of DNA synthesis by increasing mitogen-induced increase in intracellular Ca(2+) concentration.