Figure 2.

K_IR currents in arteriolar endothelial cells. Shown are mean ± SE (n = 5) current-voltage (I–V) relationships for Ba²⁺ -sensitive currents recorded from enzymatically isolated endothelial cell tubes (see [55] for more information). At membrane potentials (E_ms) negative to the K⁺ equilibrium potential (E_K), inward currents are carried by the channels (inward rectification). At membrane potentials positive to E_K, outward currents are carried by the channels, however, the outward currents diminish as the membrane becomes more positive producing a region of negative slope conductance, where hyperpolarization increases outward current flow through the channels. At normal resting E_m (5 mM K⁺ outside and 140 mM K⁺ inside, ~−30 mV), little current flows through these channels due to block by intracellular polyamines and Mg²⁺. However, membrane hyperpolarization will recruit current through the channels and amplify the initial hyperpolarization. Also shown is the shift in the I–V relationship with an increase in extracellular K⁺ (due to the shift in E_K). Note that at the resting level of E_m (−30 mV) with 15 mM K⁺ outside, there is now outward current through K_IR channels that will tend to hyperpolarize the membrane toward the new E_K. Data from [55] and graph modified from the same publication, with permission.