Vol. 278, Issue 4, H1335-H1344, April 2000
Immunochemical evidence for a unique GPI-anchored carbonic
anhydrase isozyme in human cardiomyocytes
Anja Sylvia
Knüppel-Ruppert1,
Gerolf
Gros1,
Wolfgang
Harringer2, and
Hans-Peter
Kubis1
1 Vegetative Physiologie, Zentrum Physiologie,
Medizinische Hochschule Hannover, and 2 Division
of Thoracic and Cardiovascular Surgery, Hannover Medical School,
D-30623 Hannover, Germany
To clarify the
controversial question of cell-specific distribution of carbonic
anhydrase (CA) in the heart, endothelial cells and cardiomyocytes were
isolated from porcine and human hearts and were characterized with
cell-specific markers. CA activity was found in the microsomal fraction
of both cell types. It was shown by Triton X-114 phase separation that
both cell types possess a membrane-bound form of CA. These CAs share
the same mechanism of membrane-anchoring via
glycosylphosphatidylinositol (GPI), which excludes identity with
transmembrane isoforms CA IX or CA XII. Western blotting analysis of
human microsomes with anti-human CA IV antibodies revealed a marked
difference in immunoreactivity. Endothelial CA activity resulted in
11-fold stronger CA IV bands compared with identical amounts of
myocytic CA activity, indicating that cardiac endothelium and
cardiomyocytes possess immunologically distinct forms of CA. We
conclude that in human hearts CA IV is associated with the endothelium,
whereas most of the CA in myocytes is not identical with one of the
known CA isozymes. This suggests that cardiomyocytic CA is a novel isozyme.
carbonic anhydrase activity; membrane-bound isozyme; porcine heart; human heart
