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Membrane-bound carbonic anhydrase in the heart
1Zentrum Physiologie, Medizinische Hochschule Hannover, Federal Republic of Germany.
The American Journal of Physiology
|February 1, 1992
Summary
This study found that carbonic anhydrase (CA) is primarily located in the sarcolemmal membranes of heart cells. This integral membrane protein may play a role in proton buffering within the heart.
Area of Science:
- Biochemistry
- Cell Biology
- Cardiovascular Physiology
Background:
- Carbonic anhydrase (CA) is a crucial enzyme involved in various physiological processes.
- Its localization within cardiac tissue, particularly in relation to specific membrane fractions, remains incompletely understood.
Purpose of the Study:
- To investigate the specific localization and membrane association of carbonic anhydrase (CA) within cardiac tissue.
- To determine if CA activity in heart homogenates is associated with sarcolemmal (SL) or other intracellular membranes.
Main Methods:
- Subfractionation of bovine heart microsomes using density gradient centrifugation.
- Assay of specific carbonic anhydrase (CA) activity in isolated membrane fractions.
- Determination of marker enrichment for sarcolemma, sarcoplasmic reticulum, and mitochondria.
- Triton X-114 phase separation to assess membrane integration.
- Immunofluorescence staining of rabbit heart cryosections using a CA inhibitor.
Main Results:
- Fractions enriched in sarcolemmal (SL) markers showed a significant ninefold increase in specific carbonic anhydrase (CA) activity compared to microsomes.
- CA activity in fractions enriched with sarcoplasmic reticulum or mitochondrial markers was similar to that of the initial microsomes.
- Cytosolic markers confirmed that CA activity in the SL fraction was not due to contamination.
- Triton X-114 phase separation indicated that the CA activity is associated with an integral membrane protein.
- Fluorescent staining confirmed CA presence in the sarcolemmal region of cardiomyocytes and suggested association with intracellular membranes.
Conclusions:
- The majority of carbonic anhydrase (CA) in the heart appears to be localized to the sarcolemmal (SL) membrane as an integral protein.
- While intracellular CA is present, sarcolemmal CA is likely the predominant form in cardiac tissue.
- The enzyme's role in extracellular proton buffering in the heart warrants further investigation.