Comparison of Adrenergic and Purinergic Receptor Contributions to Vasomotor Responses in Mesenteric Arteries of C57BL/6J Mice and Wistar Rats.

INTRODUCTION: The sympathetic nervous system can modulate arteriolar tone through release of adenosine triphosphate and norepinephrine, which bind to purinergic and adrenergic receptors (ARs), respectively. The expression pattern of these receptors, as well as the composition of neurotransmitters released from perivascular nerves (PVNs), can vary both in organ systems within and across species, such as mice and rats. OBJECTIVE: This study explores the function of α1A subtypes in mouse and rat third-order mesenteric arteries and investigates PVN-mediated vasoconstriction to identify which neurotransmitters are released from sympathetic PVNs. METHODS: Third-order mesenteric arteries from male C57BL/6J mice and Wistar rats were isolated and mounted on a wire myograph for functional assessment. Arteries were exposed to phenylephrine (PE) and then incubated with either α1A antagonist RS100329 (RS) or α1D antagonist BMY7378, before reexposure to PE. Electrical field stimulation was performed by passing current through platinum electrodes positioned adjacent to arteries in the absence and presence of a nonspecific alpha AR blocker phentolamine and/or P2X1-specific purinergic receptor blocker NF449. RESULTS: Inhibition of α1 ARs by RS revealed that PE-induced vasoconstriction is primarily mediated through α1A and that the contribution of the α1A AR is greater in rats than in mice. In the mouse model, sympathetic nerve-mediated vasoconstriction is mediated by both ARs and purinergic receptors, whereas in rats, vasoconstriction appeared to only be mediated by ARs and a nonpurinergic neurotransmitter. Further, neither model demonstrated that α1D ARs play a significant role in PE-mediated vasoconstriction. CONCLUSIONS: The mesenteric arteries of male C57BL/6J mice and Wistar rats have subtle differences in the signaling mechanisms used to mediate vasoconstriction. As signaling pathways in humans under physiological and pathophysiological conditions become better defined, the current study may inform animal model selection for preclinical studies.

Morphological and pharmacological characterization of the porcine popliteal artery: A novel model for study of lower limb arterial disease.

OBJECTIVE: This study was undertaken to characterize structural and pharmacological properties of the pig popliteal artery in order to develop a novel system for the examination of lower limb blood flow regulation in a variety of cardiovascular pathologies, such as diabetes-induced peripheral artery disease. METHODS: Popliteal arteries were isolated from streptozocin-induced diabetic pigs or age-matched saline-injected control pigs for morphological study using transmission electron microscopy and for examination of vasoreactivity to pharmacological agents using wire myography. RESULTS: Transmission electron microscopy of the porcine popliteal artery wall revealed the presence of endothelial cell-smooth muscle cell interactions (myoendothelial junctions) and smooth muscle cell-smooth muscle cell interactions, for which we have coined the term "myo-myo junctions." These myo-myo junctions were shown to feature plaques indicative of connexin expression. Further, the pig popliteal artery was highly responsive to a variety of vasoconstrictors including norepinephrine, phenylephrine, and U46619, and vasodilators including acetylcholine, adenosine 5'-[ß-thio] diphosphate, and bradykinin. Finally, 2 weeks after streptozocin-induced diabetes, the normalized vasoconstriction of the pig popliteal artery to norepinephrine was unaltered compared to control. CONCLUSIONS: The pig popliteal artery displays structural and pharmacological properties that might prove useful in future studies of diabetes-associated peripheral artery disease and other lower limb cardiovascular diseases.

Low intravascular pressure activates endothelial cell TRPV4 channels, local Ca2+ events, and IKCa channels, reducing arteriolar tone.

Endothelial cell (EC) Ca(2+)-activated K channels (SK(Ca) and IK(Ca) channels) generate hyperpolarization that passes to the adjacent smooth muscle cells causing vasodilation. IK(Ca) channels focused within EC projections toward the smooth muscle cells are activated by spontaneous Ca(2+) events (Ca(2+) puffs/pulsars). We now show that transient receptor potential, vanilloid 4 channels (TRPV4 channels) also cluster within this microdomain and are selectively activated at low intravascular pressure. In arterioles pressurized to 80 mmHg, ECs generated low-frequency (~2 min(-1)) inositol 1,4,5-trisphosphate receptor-based Ca(2+) events. Decreasing intraluminal pressure below 50 mmHg increased the frequency of EC Ca(2+) events twofold to threefold, an effect blocked with the TRPV4 antagonist RN1734. These discrete events represent both TRPV4-sparklet- and nonsparklet-evoked Ca(2+) increases, which on occasion led to intracellular Ca(2+) waves. The concurrent vasodilation associated with increases in Ca(2+) event frequency was inhibited, and basal myogenic tone was increased, by either RN1734 or TRAM-34 (IK(Ca) channel blocker), but not by apamin (SK(Ca) channel blocker). These data show that intraluminal pressure influences an endothelial microdomain inversely to alter Ca(2+) event frequency; at low pressures the consequence is activation of EC IK(Ca) channels and vasodilation, reducing the myogenic tone that underpins tissue blood-flow autoregulation.