ATP-sensitive K+ and Ca2+-activated K+ channels in lamprey (Petromyzonmarinus) red blood cell membrane

The patch-clamp technique was used to demonstrate the presence of ATP-sensitive K+ channels and Ca2+-activated K+ channels in lamprey (Petromyzonmarinus) red blood cell membrane. Whole-cell experiments indicated that the membrane current under isosmotic (285 mosmol l–1) conditions is carried by K+. In the inside-out configuration an ATP-sensitive K+ channel (70–80 pS inward, 35–40 pS outward) was present in 35% of patches. Application of ATP to the intracellular side reduced unitary current with half-maximal inhibition in the range 10–100 µM. A block was obtained with 100 µM lidocaine and inhibition was obtained with 0.5 mM barium acetate. A Ca2+-activated K+ channel (25–30 pS inward, 10–15 pS outward) was present in 57% of patches. Inhibition was produced by 10 mM TEA and 500 nM apamin and sensitivity to Ba2+ was lower than for ATP-sensitive channels. No spontaneous channel activity was recorded in the cell-attached configuration under isotonic conditions. With hypotonic saline 68% of patches showed spontaneous single-channel activity, and, of 75 active patches, 66 cell-attached patches showed channel activity corresponding to Ca2+-activated K+ channels.