A calcium-activated potassium channel in growth plate chondrocytes: regulation by protein kinase A

Single channel K+ currents were recorded from inside-out patches of membrane obtained from cultured chicken growth plate chondrocytes. With a symmetrical 140 mM concentration of K+ across the cell membrane, a large conductance (211 pS), outward-rectifying, K+ channel was identified. Opening of this channel was dependent on the presence of internal Ca2+ with half maximal activation of the channel occurring with 3 microM Ca2+. The channel was blocked by internal application of tetraethylammonium (IC50 = 45 mM) and 1 mM Ba2+. Application of the catalytic subunit of protein kinase A to the cytosolic membrane resulted in over a three-fold increase in the open probability for the channel. Thus, growth plate chondrocytes contain a large-conductance, Ca(2+)-activated K+ channel which can be up-regulated during stimulation of protein kinase A.