Expression of membrane-associated carbonic anhydrase XIV on neurons and axons in mouse and human brain

Abstract

Although long suspected from histochemical evidence for carbonic anhydrase (CA) activity on neurons and observations that CA inhibitors enhance the extracellular alkaline shifts associated with synaptic transmission, an extracellular CA in brain had not been identified. A candidate for this CA was suggested by the recent discovery of membrane CA (CA XIV) whose mRNA is expressed in mouse and human brain and in several other tissues. For immunolocalization of CA XIV in mouse and human brain, we developed two antibodies, one against a secretory form of enzymatically active recombinant mouse CA XIV, and one against a synthetic peptide corresponding to the 24 C-terminal amino acids in the human enzyme. Immunostaining for CA XIV was found on neuronal membranes and axons in both mouse and human brain. The highest expression was seen on large neuronal bodies and axons in the anterolateral part of pons and medulla oblongata. Other CA XIV-positive sites included the hippocampus, corpus callosum, cerebellar white matter and peduncles, pyramidal tract, and choroid plexus. Mouse brain also showed a positive reaction in the molecular layer of the cerebral cortex and granular cellular layer of the cerebellum. These observations make CA XIV a likely candidate for the extracellular CA postulated to have an important role in modulating excitatory synaptic transmission in brain.

Surface carbonic anhydrase activity on astrocytes and neurons facilitates lactate transport

“…Since most of the finer pyramidal cell processes are removed during acute dissociation, this activity could be associated with the cell body. In view of the previous immunohistochemical studies (Parkkila et al, 2001;Wang et al, 2002), this activity may be due to either CA XIV, CA IV, or both enzymes.…”

“…In hippocampal slices, the properties of extracellular CA were consistent only with extracellular type IV CA (Tong et al, 2000). Yet immunohistochemical studies of mammalian brain found CA IV localized to endothelial luminal membranes (Ghandour et al, 1992) and later noted a different extracellular variant, CA XIV, in association with neurons and axons (Parkkila et al, 2001). By contrast, a more recent immunocytochemical study noted CA IV immunoreactivity of neurons and glia in a variety of brain regions, but the relationship of this staining to cell surface CA activity remained unclear (Wang et al, 2002).…”

“…In both normal and CA II-deficient mice, Ridderstrale and Wistrand (2000) found histochemical evidence for extracellular CA in association with neuronal processes, but not perikarya. Immunohistochemical studies by Parkkila et al (2001) have associated CA XIV with neurons in both mouse and human brain. This extracellular, membrane-spanning CA isoform was found in a variety of brain regions, including white matter.…”

Three-dimensional structure of a halotolerant algal carbonic anhydrase predicts halotolerance of a mammalian homolog

“…CA XIV has been identified in several tissues including brain, liver, and kidney. In the kidney, CA XIV has been localized to the proximal convoluted tubule (40,45,46), particularly in the apical plasma membrane, i.e., brush border (46), of the S1 and S2 segments, where Ϸ90% of the bicarbonate in the renal filtrate is reabsorbed into the blood. In this process, protons secreted into the lumen, mainly by the brush border Na ϩ ͞H ϩ exchanger, protonate the luminal bicarbonate to carbonic acid that is dehydrated by a membrane-associated CA(s) to CO 2 that easily permeates the brush border membranes.…”

Carbonic anhydrase IV and XIV knockout mice: Roles of the respective carbonic anhydrases in buffering the extracellular space in brain

“…However, some residual extracellular CA activity remained after this treatment. Once it was shown immunologically to be present on neurons and axons in mouse brain (14) CA XIV became a logical candidate for this other CA.…”