BIochtmlca et Blophystca Acta, 1026 (1990) 113-116 113 Elsevaer BBAMEM 74917 Membrane specific carbonic anhydrase (CAIV) expression in human tissues N.D Carter 1, A Fryer 2, A.G. Grant 3, R. Hume 4, R.G. Strange 2 and P.J. Wlstrand 5 1 Department of Chdd Health, St George's Hospttal Medical School, London (U K), 2 Chmcal Btochemtstry Research Laboratory School of Postgraduate Medicine, Untoerslty of Keele, Staffs (U K ), 3 Department of Surgery, St George's Hospttal Medical School, London (U K ), 4 Department of ChlM L:fe and Health, Umverslty of Edinburgh, Edinburgh (U K) and 5 Institute of Medtcal Pharmacology, Uppsala (Sweden) (Received21 December1989) Key words Carbomc anhydrase, Enzymeexpression, (Human) Membrane-bound carbonic anhydrase IV (CAIV) expression has been evaluated in a range of fetal and adult human tissues and in cell culture. All tissues tested showed expression of CAIV, assessed by Western blotting, with a single immunodetected band at 55 kDa. The levels varied in fetal lung and liver during development and in various zones of the fetal brain. CAIV was dearly expressed in lung, pancreatic tumour and skin cell cultures. Introduction Carbonic anhydrase (EC 4 2 1 1), an efficient catalyst of the reaction, H20 + CO 2 ~ H++ HCO3, is present at high levels m erythrocytes and electrolyte-transport- ing epitheha where it is beheved to mediate the transfer of CO 2, H ÷, HCO~- and C1- [1] A variety of loci encode the isoenzymes identified m mammahan tissues These include CAII which is ubiquitously expressed in mammalian ceils and CAI and CAIII where expression is largely restncted to erythrocytes and skeletal muscle, respecUvely [2] More recently, mltochondnal (CAV) and sahvary (CAVI) lso- forms have been identified as well as the membrane-as- sociated enzyme, CAIV, which is the subject of this commumcatlon [2] In man, CAIV has been identified m the rmcrowlh and basal mfoldmgs of renal tubular cells and this isoform has recently been purified and charactensed [3] An apparently homologous enzyme [4] has also been purified from bovme and adult human lung It is pro- posed that the CAIV isoenzyme Is pnmanly responsible for the reabsorptxon of HCO 3- in the proximal tubule and is Involved In the formation of lung hqmd during fetal hfe We now report, for the first time, the demonstrauon of CAIV expression in a wide range of fetal, adult, Correspondence N D Carter, Department of Chtld Health, St George's Hospital Medical School, Cranmer Terrace, London, SW17 ORE, U K normal and mahgnant human cells The ubiquitous expression of the lsoenzyme has enabled us to make new proposals regarding it's function Material and Methods Source of spectmens Samples of lung, liver, kidney and brain were ob- tained w~thln 4 h of death from aborted fetuses (10-22 weeks gestation) following terrmnatlon of pregnancy, premature and term infants (24-42 weeks gestataon) who died in the neonatal pertod and infants who suffered sudden infant death syndrome Red blood cells were also taken from fetuses, neonates and infants Blood specimens were obtained from abor- tuses (10-22 weeks gestation) by cardiac puncture within 2 h of delivery and from neonates (24-42 weeks gesta- tion) by vempuncture within 24 h of birth as part of an infection screen m infants without overt neurological problems Blood samples were centrifuged at 3000 rpm at room temperature for 5 mmn and the supernatant plasma and buffy coat removed The red cells were resuspended in 154 mM NaC1 and recentnfuged The supernatant was discarded and this wash procedure repeated twine more The pellet was then stored at - 70 o C until required A careful estimate of developmental age was made m each fetus, based on size (mcludmg crown-heel, crown- rump and heel-toe measurements), menstrual history and ultrasound In neonates, gestational age was as- sessed by the Dubowltz score 0005-2736/90/$03 50 © 1990 Elsexaer ScmncePubhshers B V (BlomedmalDlvaslon)