Aquaporin-4 (AQP4) is the main water channel in the brain and primarily localized to astrocytes where the channels are thought to contribute to water and K(+) homeostasis. The close apposition of AQP4 and inward rectifier K(+) channels (Kir4.1) led to the hypothesis of direct functional interactions between both channels. We investigated the impact of AQP4 on stimulus-induced alterations of the extracellular K(+) concentration ([K(+)](o)) in murine hippocampal slices. Recordings with K(+)-selective microelectrodes combined with field potential analyses were compared in wild type (wt) and AQP4 knockout (AQP4(-/-)) mice. Astrocyte gap junction coupling was assessed with tracer filling during patch clamp recording. Antidromic fiber stimulation in the alveus evoked smaller increases and slower recovery of [K(+)](o) in the stratum pyramidale of AQP4(-/-) mice indicating reduced glial swelling and a larger extracellular space when compared with control tissue. Moreover, the data hint at an impairment of the glial Na(+)/K(+) ATPase in AQP4-deficient astrocytes. In a next step, we investigated the laminar profile of [K(+)](o) by moving the recording electrode from the stratum pyramidale toward the hippocampal fissure. At distances beyond 300 μm from the pyramidal layer, the stimulation-induced, normalized increases of [K(+)](o) in AQP4(-/-) mice exceeded the corresponding values of wt mice, indicating facilitated spatial buffering. Astrocytes in AQP4(-/-) mice also displayed enhanced tracer coupling, which might underlie the improved spatial re- distribution of [K(+)](o) in the hippocampus. These findings highlight the role of AQP4 channels in the regulation of K(+) homeostasis.
The Intervention Wheel is a population-based practice model that encompasses three levels of practice (community, systems, and individual/family) and 17 public health interventions. Each intervention and practice level contributes to improving population health. The Intervention Wheel, previously known as the Public Health Intervention Model, was originally introduced in 1998 by the Minnesota Department of Health, Section of Public Health Nursing. The model has been widely disseminated and used throughout the United States since that time. The evidence supporting the Intervention Wheel was recently subjected to a rigorous critique by regional and national experts. This critical process, which involved hundreds of public health nurses, resulted in a more robust Intervention Wheel and established the validity of the model. The critique also produced basic steps and best practices for each of the 17 interventions. Part I describes the Intervention Wheel, defines population-based practice, and details the recommended modifications and validation process. Part II provides examples of the innovative ways that the Intervention Wheel is being used in public health/public health nursing practice, education, and administration. The two articles provide a foundation and vision for population-based public health nursing practice and direction for improving population health.
In a changing and complex health care system, public health nurses face challenges to explain their work and contributions to health outcomes. In response to this need, the Minnesota Department of Health, Section of Public Health Nursing, initiated a process to describe public health nursing interventions. The Public Health Nursing Interventions (PHI) Model was developed through a collaborative process by public health nurses at the state and local levels. The purpose of the model was to define more clearly the practice of public health nursing and to describe better the work of public health nurses at the community and systems levels. The PHI model identifies 17 interventions and provides practice examples at the systems, community and individual/family levels. The model defines a broader view of the mission and scope of public health nursing. Practice examples are given for agency staff, administrators, educators, and policy makers.
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