ATP-Sensitive K+-channel Run-Down is Mg2+ Dependent

ATP-sensitive K⁺-channel currents were recorded from isolated membrane patches and voltage-clamped CRI-G1 insulin-secreting cells. Internal Mg²⁺ ions inhibited ATP-K⁺ channels by a voltage-dependent block of the channel current and decrease of open-state probability. The run-down of ATP-K⁺ channel activity was also shown to be [Mg²⁺]_i dependent, being almost abolished in Mg²⁺-free conditions. Substitution of Mn²⁺ for Mg²⁺ did not prevent run-down, nor did the presence of phosphate-donating nucleotides, a protease or phosphatase inhibitor or replacement of Cl^- by gluconate.