Physiologic Influences of Transepithelial K+ Secretion

Cellular ionic balance relies on ion channels and coupled transporters to maintain and use the transmembrane electrochemical gradients of the cations Na+ and K+. High intracellular K+ concentration provides a ready reserve within the body allowing epithelia to secrete K+into the fluid covering the apical membrane in the service of numerous physiologic activities. A major role for transepithelial K+ secretion concerns the balance of total body K+ such that excretion of excess K+ in the diet safeguards against disturbances to cellular balance. Accomplishing this transepithelial flow involves two archetypical cellular mechanisms, Na+ absorption and Clr secretion. Ion channels for K+, Na+, and Clr , as well as cotransporters, exchangers, and pumps contribute to produce transepithelial flow by coupling electrochemical gradients such that K+ flow enters across the basolateral membrane and exits through the apical membrane. Beyond excretion, transepithelial K+ secretion serves to create the high K+ concentration of endolymph in the inner ear that supports sensation of sound and body orientation. For several epithelia such as those in airways and gastric mucosa, the elevated K+ concentration of apical fluid may occur largely as a consequence of supporting the secretion of other ions such as Clr or H+. Less well-appreciated consequences of K+ secretion may result as in saliva and colonic luminal fluid where a high K+ concentration likely influences interactions with the resident microbiome. Independent control of K+ secretion also allows for specific adjustments in rate that serve the physiology of organs large and small

Determinants of “return to work in good health” among workers with back pain who consult in primary care settings: a 2-year prospective study

Many factors have been linked to return to work after a back pain episode, but our understanding of this phenomenon is limited and cross-sectional dichotomous indices of return to work are not valid measures of this construct. To describe the course of “return to work in good health” (RWGH—a composite index of back pain outcome) among workers who consulted in primary care settings for back pain and identify its determinants, a 2-year prospective study was conducted. Subjects (n = 1,007, 68.4%) were workers who consulted in primary care settings of the Quebec City area for a nonspecific back pain. They completed five telephone interviews over 2 years (follow-up = 86%). Analyses linking baseline variables with 2-year outcome were conducted with polytomous logistic regression. The proportion of “success” in RWGH increased from 18% at 6 weeks to 57% at 2 years. In women, persistent pain, pain radiating to extremities, increasing job seniority, not having a unionized job, feeling that the physician did listen carefully and increasing fear-avoidance beliefs towards work and activity were determinants of “failure” in RWGH. In men, decreasing age, cigarette smoking, poor self-reported health status, pain in the thoracic area, previous back surgeries, a non-compensated injury, high pain levels, belief that job is below qualifications, likelihood of losing job, job status, satisfaction with health services and fear-avoidance beliefs towards work were all significant. RWGH among workers with back pain receives multiple influences, especially among men. In both genders, however, fear-avoidance beliefs about work are associated with failure and high self-efficacy is associated with success