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The GLUT4 glucose transporter is primarily expressed in skeletal muscle, heart and adipose tissue, where its expression is postnatal, coincident with the acquisition of insulin-regulated glucose transport. In muscle, contraction also regulates GLUT4 activity in the postnatal animal. Here we demonstrate that GLUT4 is expressed in the developing mouse embryo with specific tissue and spatiotemporal patterns. From embryonic day 9 (E9; E1 = day of copulation plug) to postnatal day 70 (P70), mice were analyzed for GLUT4 mRNA and protein expression by in situ hybridization, immunohistochemistry and immunoblot. Specificity was confirmed with sense riboprobe hybridization and peptide competition, respectively. At E9, GLUT4 was detected in the cranial neural folds in the outer (mantle) layer of the neuroepithelium. At E10, expression was present throughout the developing heart and was prominent in the endocardial cushions through E12. At E10–12, GLUT4 was also prominent in craniofacial mesenchyme. GLUT4 expression in cartilage and bone was evident at E12 and was maintained throughout early postnatal life. GLUT4 was apparent throughout embryonic development in the ventricular epithelium, choroid plexus and in the developing cerebellum. At birth, cardiac expression was reduced and GLUT4 was most evident in cartilage, bone and specific brain regions. In the latter, GLUT4 expression was most evident in the cerebellum, specifically in the external granular layer through P7 and in the internal granular layer thereafter. Maximal GLUT4 protein levels in the cerebellum were measured between P14 and P21 and were reduced in the adult brain. These findings suggest that GLUT4-mediated glucose transport may play important roles during development of the brain and nonneuronal tissues in the mouse embryo.

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Discussion The quantitative carbon dioxide analyser is one of the most valuable monitors we have in clincial anaesthesia. Unfortunately, because of their size and cost, these monitors are not available in all areas where tracheal intuhation is carried out. Few hospitals can supply every operating room, emergency room or "crash cart" with one of these devices, and they are not practical for use by medical personnel in "field" settings or by paramedics in their work environment. The pH-sensitive chemical indicator, on the other hand, is small, inexpensive and easy to use, and would be ideal for all the above situations. It is not a replacement for the quantitative carbon dioxide analyser, but if used in conjunction with the usual methods of detecting correct tube placement, it should reduce the number of undiagnosed oesophagcal intubations. References t PotlardBJ, Juntas F. Accidental intubatian of the oesophagus.

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