When arteries constrict to agonists, the endothelium inversely responds, attenuating the initial vasomotor response. The basis of this feedback mechanism remains uncertain, although past studies suggest a key role for myoendothelial communication in the signaling process. The present study examined whether second messenger flux through myoendothelial gap junctions initiates a negative-feedback response in hamster retractor muscle feed arteries. We specifically hypothesized that when agonists elicit depolarization and a rise in second messenger concentration, inositol trisphosphate (IP₃) flux activates a discrete pool of IP₃ receptors (IP₃Rs), elicits localized endothelial Ca²⁺ transients, and activates downstream effectors to moderate constriction. With use of integrated experimental techniques, this study provided three sets of supporting observations. Beginning at the functional level, we showed that blocking intermediate-conductance Ca²⁺-activated K⁺ channels (IK) and Ca²⁺ mobilization from the endoplasmic reticulum (ER) enhanced the contractile/electrical responsiveness of feed arteries to phenylephrine. Next, structural analysis confirmed that endothelial projections make contact with the overlying smooth muscle. These projections retained membranous ER networks, and IP₃Rs and IK channels localized in or near this structure. Finally, Ca²⁺ imaging revealed that phenylephrine induced discrete endothelial Ca²⁺ events through IP₃R activation. These events were termed recruitable Ca²⁺ wavelets on the basis of their spatiotemporal characteristics. From these findings, we conclude that IP₃ flux across myoendothelial gap junctions is sufficient to induce focal Ca²⁺ release from IP₃Rs and activate a discrete pool of IK channels within or near endothelial projections. The resulting hyperpolarization feeds back on smooth muscle to moderate agonist-induced depolarization and constriction.

Chronic inflammation is rapidly becoming recognized as a key contributor to numerous pathologies. Despite detailed investigations, understanding of the molecular mechanisms regulating inflammation is incomplete. Knowledge of such critical regulatory processes and informative indicators of chronic inflammation is necessary for efficacious therapeutic interventions and diagnostic support to clinicians. We used a computational modeling approach to elucidate the critical factors responsible for chronic inflammation and to identify robust molecular indicators of chronic inflammatory conditions. Our kinetic model successfully captured experimentally observed cell and cytokine dynamics for both acute and chronic inflammatory responses. Using sensitivity analysis, we identified macrophage influx and efflux rate modulation as the strongest inducing factor of chronic inflammation for a wide range of scenarios. Moreover, our model predicted that, among all major inflammatory mediators, IL-6, TGF-β, and PDGF may generally be considered the most sensitive and robust indicators of chronic inflammation, which is supported by existing, but limited, experimental evidence.

This study presents a multicellular computational model of a rat mesenteric arteriole to investigate the signal transduction mechanisms involved in the generation of conducted vasoreactivity. The model comprises detailed descriptions of endothelial (ECs) and smooth muscle (SM) cells (SMCs), coupled by nonselective gap junctions. With strong myoendothelial coupling, local agonist stimulation of the EC or SM layer causes local changes in membrane potential (V_m) that are conducted electrotonically, primarily through the endothelium. When myoendothelial coupling is weak, signals initiated in the SM conduct poorly, but the sensitivity of the SMCs to current injection and agonist stimulation increases. Thus physiological transmembrane currents can induce different levels of local V_m change, depending on cell's gap junction connectivity. The physiological relevance of current and voltage clamp stimulations in intact vessels is discussed. Focal agonist stimulation of the endothelium reduces cytosolic calcium (intracellular Ca²⁺ concentration) in the prestimulated SM layer. This SMC Ca²⁺ reduction is attributed to a spread of EC hyperpolarization via gap junctions. Inositol (1,4,5)-trisphosphate, but not Ca²⁺, diffusion through homocellular gap junctions can increase intracellular Ca²⁺ concentration in neighboring ECs. The small endothelial Ca²⁺ spread can amplify the total current generated at the local site by the ECs and through the nitric oxide pathway, by the SMCs, and thus reduces the number of stimulated cells required to induce distant responses. The distance of the electrotonic and Ca²⁺ spread depends on the magnitude of SM prestimulation and the number of SM layers. Model results are consistent with experimental data for vasoreactivity in rat mesenteric resistance arteries.

Wound fibrosis (i.e., excessive scar formation) is a medical problem of increasing prevalence, with poorly understood mechanistic triggers and limited therapeutic options. In this study, we employed an integrated approach that combines computational predictions with new experimental studies in mice to identify plausible mechanistic triggers of pathological scarring in skin wounds. We developed a computational model that predicts the time courses for six essential cell types, 18 essential molecular mediators, and collagen, which are involved in inflammation and proliferation during wound healing. By performing global sensitivity analyses using thousands of model-simulated wound-healing scenarios, we identified five key processes (among the 90 modeled processes) whose dysregulation may lead to pathological scarring in wounds. By modulating a subset of these key processes, we simulated fibrosis in wounds. Moreover, among the 18 modeled molecular mediators, we identified TGF-β and the matrix metalloproteinases as therapeutic targets whose modulation may reduce fibrosis. The model predicted that simultaneous modulation of TGF-β and matrix metalloproteinases would be more effective in treating excessive scarring than modulation of either therapeutic target alone. Our model was validated with previously published and newly generated experimental data, and suggested new in vivo experiments.