Magnesium Modulates ROMK Channel–Mediated Potassium Secretion

[摘要] The ability of intracellular and extracellular Mg2+ to block secretory K+ currents through ROMK channels under physiologic conditions is incompletely understood. We expressed ROMK2 channels in Xenopus oocytes and measured unitary currents in the inside-out and cell-attached modes of the patch-clamp technique. With 110 mM K+ on both sides of the membrane, 0.2 to 5 mM Mg2+ on the cytoplasmic side reduced outward currents, but not inward currents, at V m > 0. With 11 or 1.1 mM extracellular K+ ([K+]o), ≥0.2 mM Mg2+ blocked outward currents in the physiologic V m range (0 to −60 mV). With decreasing [K+]o, the apparent dissociation constant of the blocker decreased, but the voltage dependence of block did not significantly change. Whole-cell recordings from principal cells of rat cortical collecting ducts revealed similar inhibitory effects of intracellular Mg2+. Mg2+ added to the extracellular solution also reduced single-channel currents with an affinity that increased as [K+]o decreased. In conclusion, physiologic concentrations of intracellular and extracellular Mg2+ can influence secretory K+ currents through ROMK channels. These effects could play a role in the modulation of K+ transport under conditions of K+ and/or Mg2+ depletion.

[学科分类] 泌尿医学