Carbon monoxide (CO) and hydrogen sulphide are a gaseous vasodilators produced in the vascular wall by the enzymes heme oxygenase (HO) and cystathionine γ-lyase, respectively. Elucidating mechanisms by which these gases induce vasodilation improves understanding of physiological control of vascular contractility and could lead to the development of novel therapies for cardiovascular diseases, including hypertension and stroke. I will summarize our recent studies and compare and contrast mechanisms by which CO and H2S modulate arterial smooth muscle cell ion channel activity to dilate cerebral arterioles. Our data indicate that HO-2-derived CO activates large-conductance calcium (Ca2+) activated potassium (BKCa) channels by binding to reduced inhibitory heme attached to a conserved heme-binding domain in the channel C-terminus. CO binding to heme elevates BKCa channel apparent Ca2+-sensitivity, leading to enhanced coupling to Ca2+ sparks in piglet cerebral arteriole smooth muscle cells. The elevation in coupling increases transient BKCa current frequency and amplitude, leading to membrane hyperpolarization, a reduction in voltage-dependent Ca2+ channel activity, a decrease in global intracellular Ca2+ concentration ([Ca2+]i) and vasodilation. Glutamate stimulates CO production by wild-type astrocytes (HO-2+/+), but not by astrocytes of HO-2 knock out (HO-2-/-) mice. Glutamate does not affect BKCa channel activity in smooth muscle cells alone, but activates single BKCa channels and transient BKCa currents in smooth muscle cells that are in contact with astrocytes. HO-2 inhibition or genetic ablation of HO-2 prevents glutamate-induced BKCa channel activation. In brain slices, glutamate activates Ca2+ sparks and reduces global [Ca2+]i in arteriole myocytes, leading to vasodilation, and these effects are blocked by HO-2 inhibition. Brain slice arteriole dilation to glutamate is blocked by astrocyte toxin and BKCa inhibition. Collectively, data indicate that endogenous CO binds to heme on BKCa channels, leading to enhanced coupling to Ca2+ sparks in arteriole smooth muscle cells. In the neurovascular unit, glutamate-induced astrocyte-derived CO produces vasodilation to couple blood flow to increased neuronal activity. In contrast to the relatively selective mechanism of vasodilation activated by CO, our data indicate that H2S dilates cerebral arterioles by activating both ATP-sensitive potassium (KATP) and BKCa channels in piglet cerebral arteriole smooth muscle cells. Pinacidil, a KATP channel activator, and H2S activate K+ currents at physiological steady-state voltages in cerebral arteriole smooth muscle cells. Glibenclamide, a selective KATP channel inhibitor, fully reverses pinacidil-induced K+ currents, but only partially reverses H2S-induced K+ currents. Pinacidil dilates pressurized (40 mmHg) piglet arterioles and glibenclamide fully reverses this effect. Na2S also dilates cerebral arterioles, but this is only partially reversed by glibenclamide. Western blotting indicates that cerebral arterioles express Kir6.1 and sulfonylurea receptor 2B (SUR2B) KATP channel subunits. Pinacidil and H2S-induced vasodilation is smaller in cerebral arterioles of SUR2 null mice than in wild-type controls. Based on these data, we tested the hypothesis that H2S dilates cerebral arterioles by modulating local and global intracellular Ca2+ signals in smooth muscle cells. High-speed confocal imaging revealed that H2S increases Ca2+ spark frequency and decreases global intracellular Ca2+ concentration ([Ca2+]i) in cerebral arteriole smooth muscle cells. H2S does not alter Ca2+ wave frequency. H2S increases the frequency of transient BKCa currents, but does not alter the amplitude of these events. In contrast, H2S does not alter the activity of single KCa channels recorded in the absence of Ca2+ sparks. H2S elevates SR Ca2+ load ([Ca2+]SR), which leads to Ca2+ spark activation in arterial smooth muscle cells. H2S also hyperpolarizes the membrane potential of pressurized arterioles and this is partially reversed by iberiotoxin, a selective BKCa channel blocker. Iberiotoxin and ryanodine, a ryanodine receptor inhibitor, also partially reverse H2S-induced vasodilation. In summary, these data indicate that H2S can dilate cerebral arterioles by activating both KATP channels containing SUR2B subunits and by stimulating Ca2+ sparks, which activate BKCa channels, in arterial smooth muscle cells. Collectively, these studies provide evidence that astrocyte-derived CO and H2S, an endothelial-derived gas transmitter, dilate cerebral arterioles through distinct signaling mechanisms that activate ion channels in smooth muscle cells.