title: Heterogeneity of intracellular potassium activity and membrane potential in hypoxic guinea pig ventricle.
abstract: The relationship between membrane potential (Em) and the potassium equilibrium potential (EK) was investigated in hypoxic guinea pig papillary muscle. After more than 8 hours of hypoxia, cells with near normal Em (-86.2 +/- 0.9 mV) and action potentials were observed. However, the intracellular potassium concentration ([K+]i) based on chemical analysis and the assumption that potassium was homogeneously distributed was 41.8 +/- 4.3 mM; the apparent EK was -55.7 +/- 2.9 mV, significantly positive to Em. Measurements with potassium ion-selective microelectrodes revealed that prolonged hypoxia results in at least two populations of cells with different characteristics. The first population had an intracellular potassium activity (aiK) of 101.5 +/- 1.9 mM, and EK was 4.7 mV negative to Em. In contrast, EK was 33.4 +/- 1.3 mV negative to Em in the second population. These cells also exhibited a reduced sensitivity to changes in bath potassium, and calculations suggest aiK was about 18 mM. The existence of cell populations with a near normal and very low aiK can explain the intermediate value of [K+]i calculated assuming a homogenous potassium distribution. Cells with near normal Em and action potentials represent the population with near normal aiK. Hypoxia may also cause non-uniform changes in other cellular characteristics.
mesh_terms: D000818:Animals; D005260:Female; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology*; D007425:Intracellular Membranes / Q000378:metabolism*; D007474:Ion Exchange; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D010100:Oxygen / Q000502:physiology; D010210:Papillary Muscles / Q000503:physiopathology; D011188:Potassium / Q000378:metabolism*
chemical_list: D011188:Potassium; D010100:Oxygen