Fig. 10. Ca²⁺ action potentials are more easily evoked in mouse SLO2 KO ASM cells.

(A) Membrane potential changes recorded under current clamp mode from an aortic ASM cell freshly isolated from a 7-week old wild-type mouse (left) or Slo2 KO mouse (right). Hyperpolarizing and depolarizing currents were injected from −150 pA to 250 pA. Dotted black lines indicate 0 mV. Red traces are membrane potential responses after injecting 250 pA currents (~20 pA/pF). Graded Ca²⁺ action potentials were evoked after injecting 100 pA currents for Slo2 KO cells (7 out of 11 cells); however the same current evoked action potentials in 0 out of 12 wild-type cells. (B) Membrane potential changes recorded under current clamp mode from a femoral ASM cell freshly isolated from a 7-week old wild-type mouse (left) or Slo2 KO mouse (right). The red traces are the membrane potential responses after injecting 250 pA (~20 pA/pF) currents. Graded Ca²⁺ action potentials were evoked after injecting 100 pA current in Slo2 KO cells (14 out of 19 cells); however the same current evoked action potentials in 0 out of 11 wild-type cells. Action potentials became more regular when injecting more depolarizing currents. Evoked action potentials from Slo2 KO ASM cells were eliminated by the calcium channel blocker verapamil (10 μM). Note: there was no statistical difference in the size of wild-type and KO ASM cells. (C) Ang II makes wildtype arterial smooth muscle cells more excitable. Representative membrane potential changes were recorded under current clamp mode from an aortal smooth muscle cell freshly isolated from a 7-week wild-type mouse. Hyperpolarizing and depolarizing currents were injected from −150 pA to 150 pA at 50 pA increments. Dotted black lines indicate −50 mV. After injecting 150 pA currents (the red traces), no obvious action potentials were observed in the absence of Ang II (left) while regular Ca²⁺ action potentials were evoked in the presence of 1 μM Ang II (right). In 3 out of 5 cells, Ang II increased the cell excitability. For experiments shown in this figure, the pipette solution contained (in mM): 110 K-Gluconate, 30 KCl, 10 NaCl, 1 MgCl₂, 1 CaCl₂, 5 EGTA, 10 HEPES, pH 7.3. Under these conditions the intracellular Ca²⁺ was buffered at approximately 100 nM. The bath solution contained (in mM): 150 NaCl, 5 KCl, 2 MgCl₂, 1 CaCl₂, 10 HEPES, pH=7.3.