<prompt> If this cell were permeable only to K, what would be the effect of reducing the extracellular K concentration from 5 to 2.5 millimolar? Intracellular mM Extracellular mM 140 K 5 K 12 Na 145 Na 5 CI- 125 CI- 0.0001 Ca 5 Ca19 millivolts depolarization19 millivolts hyperpolarization38 millivolts depolarization38 millivolts hyperpolarization  <response>: If a membrane is permeable to only a single ion Vm is equal to the equilibrium potential for that ion. In this hypothetical cell, EK 88 millivolts. If the extracellular K concentration is reduced by half, EK 61 x log 2.5140 107 millivolts, Hyperpolarisation of 19 millivolts. 