Introduction Peripheral artery disease (PAD) is a highly morbid condition in which impaired blood flow to the limbs leads to pain and tissue loss. Previously we identified 670 nm electromagnetic energy (R/NIR) to increase nitric oxide levels in cells and tissue. NO elicits relaxation of smooth muscle (SMC) by stimulating potassium efflux and membrane hyperpolarization. The actions of energy on ion channel activity have yet to be explored. Here we hypothesized R/NIR stimulates vasodilation through activation of potassium channels in SMC. Methods Femoral arteries or facial arteries from C57Bl/6 and Slo1-/- mice were isolated, pressurized to 60 mmHg, pre-constricted with U46619, and irradiated twice with energy R/NIR (10 mW/cm2 for 5 min) with a 10 min dark period between irradiations. Single-channel K+ currents were recorded at room temperature from cell-attached and excised inside-out membrane patches of freshly isolated mouse femoral arterial muscle cells using the patch-clamp technique. Results R/NIR stimulated vasodilation requires functional activation of the large conductance potassium channels. There is a voltage dependent outward current in SMC with light stimulation, which is due to increases in the open state probability of channel opening. R/NIR modulation of channel opening is eliminated pharmacologically (paxilline) and genetically (BKca α subunit knockout). There is no direct action of light to modulate channel activity as excised patches did not increase the open state probability of channel opening. Conclusion R/NIR vasodilation requires indirect activation of the BKca channel.

Over 8 million Americans are treated for symptoms related to peripheral artery disease (PAD). Risk factors for PAD have been directly related to a reduction in NOS expression and NO production. Light irradiation at the far red/near infrared region (670 nm (R/NIR)) can stimulate angiogenesis by increasing NO independent of NOS through release of NO from nitrosyl‐heme stores. We hypothesized R/NIR can stimulate vasodilation, and serve as a potential therapy to improve endothelial function. Methods: Human umbilical vein endothelial cells (HUVEC) were loaded with DAF‐2 and stimulated with R/NIR at 25mW, 50mW, and 75mW up to 12J. NO was measured using HPLC of DAF‐2T. Facial arterioles from c57Bl/6 mice and human coronary arterioles from patients with and without atherosclerosis were pressurized to 60mmHg and pre‐constricted. Vessels were irradiated with 670 nm light (10mW/cm2) up to 5 min at a time with 10 min dark period between irradiation. Results: R/NIR stimulated a 26.83% (± 6.99, p<0.05) increase in NO over control. Preincubation with c‐PTIO, a NO scavenger, completely abolished R/NIR stimulated NO. In mice, vessel diameter increased 17.8% (±3.0, p<0.05) after R/NIR exposure. In vessels denuded prior to R/NIR dilation, vasodilation was abolished (1.2%, ± 2.21, p<0.001), suggesting R/NIR vasodilation was endothelial dependent. Pre‐incubation with 1mM L‐NAME did not significantly attenuate dilation (13.74% ±2.2), however c‐PTIO (100µM) could successfully block dilation (‐.51% ± 1.1, p<0.001). R/NIR significantly increased in coronary arterioles from patients with atherosclerosis 24.5% (±2.1%, p<0.01) and without atherosclerosis 44.8% (±6.2%, p<0.01). Conclusion: R/NIR can stimulate vasodilation in human and murine vessels. This vasodilation is endothelium and NO dependent, but does not require functional nitric oxide synthase. The exact source for the NO increase is unknown, but intracellular nitrosyl heme moieties should be considered as a previously unexplored source for NO.

Over 8 million Americans are treated for symptoms related to peripheral artery disease (PAD), such as intermittent claudication, impaired wound healing, and critical limb ischemia. We have shown light irradiation at the far red/near infrared region (670 nm (R/NIR)) can stimulate angiogenesis by increasing NO independent of NOS through release of NO from nitrosyl‐heme stores. We hypothesized R/NIR can stimulate vasodilation through increases in large conductance potassium channel (BKCa) activity. To test vasodilation, facial arteries from C57Bl/6 mice were isolated, pressurized to 60mmHg, and pre‐constricted with U46619 in the dark. The vessels were irradiated with 670 nm light (10mW/cm2) up to 5 min at a time with 10 min dark period between irradiation. Vessel diameter increased up to 17.8% (±3.0, p<0.05) after 5 min of R/NIR exposure. The effect of red light on single channel BKCa current was determined in enzymatically dissociated murine femoral arterial muscle cells, using the patch clamp technique and symmetrical KCl [145mM] recording solution at a patch potential of +60 mV (RT). Exposure of cell attached patches to light ( λ =670 nm, 10 mW/cm2) markedly increased the opening frequency of the large conductance potassium channels (BKCa) single channel current. This effect of light on BKCa single channel current activity could be the underlying mechanism for the vasodilatory action of red light in isolated murine femoral arterial segments. Conclusion: R/NIR exposure acts to stimulate vasodilation, by increasing the opening frequency of BKCa single channel current recorded in cell attached patches of femoral arterial smooth muscle cells.