Fig. 4. IK_Na (SLO2) in both conduit (aorta) and resistance (femoral and mesentery) rat ASM cells.

(A) Whole cell currents recorded from an acutely isolated rat aortic smooth muscle cell. Recording protocols and conditions are described in Fig. 2 legend. The control currents (top) were recorded in bath solution containing 150 mM Na⁺. Replacing extracellular Na⁺ with choline (0 Na⁺) markedly reduced the magnitude of outward currents. The IK_Na portion of current (bottom) was isolated by subtraction of the current recorded in 0 [Na⁺]_out from the control current. The bottom panel shows the normalized I–V relationships of above currents measured during the last 50 ms of each voltage step. At −20 mV, the IK_Na portion of total outward current was 72.6±2.42% (n=10). (B,C) Whole cell currents of an acutely isolated rat femoral or mesentery smooth muscle cell recorded under conditions similar to A. At −20 mV, the IK_Na portion of current was 60.3±4.59% of total outward current in femoral (n=5), or 66.7±4.36% of total outward current in mesentery (n=7). IK_Na was observed to contribute a large percentage (>50%) of outward current in both conduit and resistance arteries, and in both mice and rats.