Low Ca²⁺-sensitive maxi-K⁺ channels in human cultured fibroblasts

The patch clamp technique was used to reveal single channel activity in the membrane of human cultured fibroblasts. The most frequently detected ion channel type was a Ca²⁺-dependent K⁺ channel with a conductance of 287±38 pS in symmetrical 130 mM KCl. The channel showed a peculiar low Ca²⁺-sensitivity compared to that of similar channels in other preparations. In fact micromolar values of internal Ca²⁺ were not effective in the channel activation, except at high depolarizing membrane potentials. The activity was highly increased only when the channel was exposed to relatively high internal Ca²⁺ concentrations (0.2-2.0 mM).