The effects of aging on carbonic anhydrase concentrations in rat liver and skeletal muscle

Sexual dimorphism in LEC rat liver: suppression of carbonic anhydrase III by copper accumulation during hepatocarcinogenesis

We examined age-related changes in the protein expression of carbonic anhydrase III (CAIII) in livers of Long-Evans with a cinnamon-like color (LEC) rats using an agouti color (LEA) rats as controls. The levels of the protein of CAIII in the liver of LEC male rats increased before 20 weeks of age, at the stage of acute hepatitis, and were decreased at 54 weeks of age, while those of CAIII in the liver of LEA male rats were highly expressed at all ages. In the normal LEA rats, CAIII showed sexual dimorphism. The level of CAIII in LEA male rat liver relative to female was four times higher. On the other hand, young LEC rat (at 4-12 weeks) showed a higher protein level of CAIII than LEA rats, and then decreased during development of hepatitis. CAIII mRNA also decreased in the LEC rat liver during hepatocarcinogenesis. The level of CAIII in the tumor region was lower than that in the tumor-free region. Immunohistochemical analysis showed that glutathione S-transferase P (GST-P) was positive and CAIII was negative in the precancerous region. The expression of CAIII was suppressed in cancerous lesions in hepatoma-bearing LEC rat liver compared to uninvolved surrounding tissues. These results indicated that suppression of CAIII accompanied hepatocarcinogenesis and it is a secondary consequence of the high copper levels in the liver.

Identification of the zinc-binding protein specifically present in male rat liver as carbonic anhydrase III

A zinc (Zn)-binding protein that is present specifically in the livers of male adult rats was detected by HPLC with in-line detection by mass spectrometry (ICP MS). The Zn-binding protein was purified on Sephadex G-75 and G3000SW HPLC columns. and was identified as carbonic anhydrase III (CAIII) based on the amino acid sequence of a peptide obtained on lysyl endopeptidase digestion. CAIII is expressed as one of the major Zn-binding proteins in the livers of male rats in an age-dependent manner, a comparable amount of Zn to that of copper, Zn-superoxide dismutase (Cu,Zn-SOD) being bound to CAIII at 8 weeks of age. Castration at 4 or 8 weeks of age was shown to reduce Zn bound to CAIII to 47.5% of the sham-operated control level, suggesting that the sex-dependent expression of CAIII is partly regulated by a sex hormone, androgen. The concentration of CAIII in the livers of Long-Evans rats with a cinnamon-like coat color (LEC rats), an animal model of Wilson disease, was also estimated as Zn bound to CAIII and shown to be lower than that in Wistar rats before the onset of hepatitis. The concentration of CAIII was decreased specifically by repeated injections of cupric ions without the Cu,Zn-SOD concentration being affected.

Determination and developmental changes in carbonic anhydrase III in swine liver

1. CA-III was measured by enzyme-immunoassay in the livers of male and female swine aged from the fetus to 5 years old. 2. No sexual dimorphism in porcine liver could be detected at 6 months, but stag showed twice as much as swine of the same age. 3. The concentration of CA-III in the liver increased during development up to 6 months of age, followed by decline due to senescence.

Expression of hepatic mitochondrial carbonic anhydrase V

We have raised specific (rabbit anti-rat) polyclonal antibodies to hepatic mitochondrial carbonic anhydrase V (CA V) and used them to assay the amounts of protein expressed in liver mitochondria isolated from term-foetal, control or diabetic adult rats and in perivenous and periportal rat hepatocytes. The levels of CA V expressed in mitochondria isolated from the livers of adult male and female rats are similar and increase (about 2-fold) in mitochondria from adult diabetic rats when compared to those isolated from the livers of control rats. The level of enzyme in adult liver was higher than in the livers of term-foetal rats. CA V is expressed in both perivenous and periportal hepatocytes, but the level of expression is greater (approx. 40%) in perivenous cells. The implications and significance of these findings are discussed with reference to the roles and properties of the other carbonic anhydrase isoenzymes and the metabolic function of the mitochondrial isoenzyme.

Acetazolamide-insensitive carbonic anhydrase activities in liver and tonic skeletal muscle of adult male rats with streptozotocin-induced diabetes mellitus

One of the four discrete isoenzymes of carbonic anhydrase hitherto characterized, CA III, has the lowest turnover rate and the greatest resistance to inhibition by sulphonamides. Streptozotocin-induced diabetes mellitus resulted in a reduction in acetazolamide-resistant activity of carbonic anhydrase in the liver, but not in tonic skeletal muscle, of adult male rats. The hepatic activity declined with apparent first-order kinetics [calculated rate constant (k) 0.089 day-1] to a minimum of approx. 6% of control values; the reduction in activity was moderated by administration of insulin.

Differential regulation of hepatic carbonic anhydrase isozymes in the streptozotocin-diabetic rat

Most work with the male rat liver carbonic anhydrase isozymes in the past decade has centered on the cytosolic CA III and the mitochondrial CA V. This paper reports that the relative activity of both isozymes is altered in streptozotocin-diabetes. Carbonic anhydrase activity of perfused liver homogenates and disrupted, isolated mitochondria was measured by the mass spectrometric 18O decay technique at 37 degrees C. The contributions of the different isozymes were determined based on intracellular location and sensitivity to acetazolamide inhibition. Diabetes resulted in a twofold increase in the activity of CA V but a halving in the activity of CA III. This is the first time that liver CA V has been shown to be altered by physiological stress. The total carbonic anhydrase activity in the diabetic rat liver was unaltered compared with control rats; however, CA III never accounted for more than 50% of this activity. Since CA isozymes I, II, and IV together account for 30% of the CA activity in control rats and 70% in diabetic rats it is concluded that one or more of these isozymes is subject to regulation in the diabetic male rat. The increase in CA V during diabetes is in accord with this isozyme having an important function in provision of substrate for hepatic gluconeogenesis and ureagenesis.

Induction of carbonic anhydrase III mRNA and protein by denervation of rat muscle

Carbonic anhydrase III (CAIII) protein and mRNA amounts in fast- and slow-twitch rat muscles were examined after resection of the sciatic nerve. Striking changes occur in the fast-twitch anterior tibialis (AT) and extensor digitorum longus (EDL) muscles, where CAIII protein and mRNA are increased several-fold 16 days after denervation. The data suggest that these changes are regulated in part by changes in gene transcription and that they perhaps signal a fast-to-slow fibre type transition in these denervated muscles. AT and EDL show some differences in the effects of denervation, which are suggestive of variation in the timing of denervation-induced responses and/or the CAIII protein/mRNA turnover rates in the two muscles.