Magnesium-independent activation of inward-rectifying K+channels inVicia fabaguard cells

Abstract

The activation of inward‐rectifying K⁺ channels in guard cells at membrane potentials negative of the K⁺ equilibrium potential is important for their cellular function as proton pump‐driven K⁺ uptake pathways during stomatal opening. In animal cells the voltage‐dependence of inward‐rectifying K⁺ channels is produced to a large extent by intracellular magnesium block. In guard cells, when cytosolic Mg²⁺ was either 3 mM or < I μM, activation times, deactivation times and the steady‐state voltage‐dependence of K⁺ channels remained unchanged. It is discussed that the activation mechanism of inward‐rectifying K⁺ channels in guard cells is independent of intracellular Mg²⁺ block.