THE modulation of the activity of Ca2+-activated K + (BK) channels by activators of protein kinases A and C, respectively, was studied in cell-attached patches on isolated Müller (retinal glial) cells from rabbits. The BK channel activity was stimulated by membrane depolarization and by increasing of the intracellular Ca2+ concentration. Extracellular exposure to dibutyryl-cAMP, known to stimulate the protein kinase A, increased the open probability of the channels. Exposure to a phorbol ester, as an activator of protein kinase C, strongly reduced the channel activity whereas exposure to the protein kinase inhibitor, staurosporine, stimulated the channel activity. As glial BK channels are modulated in an opposite manner by protein kinases A and C, they may act as a cellular focus of integration of the inputs from different signaling pathways.