SciELO - Scientific Electronic Library Online

 
vol.33 issue3-4Biochemical characterization and inhibitory effects of dinophysistoxin-1, okadaic acid and microcystine l-r on protein phosphatase 2a purified from the mussel Mytilus chilensis.Reduced oxygen diffusion across the shell of Gray gull (Larus modestus) eggs author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

Related links

Share


Biological Research

Print version ISSN 0716-9760

Biol. Res. vol.33 n.3-4 Santiago  2000

http://dx.doi.org/10.4067/S0716-97602000000300006 

Carbonic anhydrase activity in the red blood cells of sea
level and high altitude natives

JORGE GAMBOA, RICARDO CACEDA, ALFREDO GAMBOA, CARLOS MONGE-C.

Laboratorio de Transporte de Oxígeno, Departamento de Ciencias Fisiológicas, Universidad Peruana Cayetano Heredia.

ABSTRACT

Red blood cell carbonic anhydrase (CA) activity has not been studied in high altitude natives. Because CA is an intraerythocytic enzyme and high altitude natives are polycythemic, it is important to know if the activity of CA per red cell volume is different from that of their sea level counterparts. Blood was collected from healthy subjects living in Lima (150m) and from twelve subjects from Cerro de Pasco (4330m), and hematocrit and carbonic anhydrase activity were measured. As expected, the high altitude natives had significantly higher hematocrits than the sea level controls (p=0.0002). No difference in the CA activity per milliliter of red cells was found between the two populations. There was no correlation between the hematocrit and CA activity.

Key words: Carbonic anhydrase, hypoxia, polycythemia.

Carbonic anhydrase (CA) is a common enzyme, and it is contained in key regulatory organs. The carotid bodies respond to hypoxia with an increase in pulmonary ventilation; see Iturriaga (1993) for a review of the mechanisms of this response. In the kidney (Swenson, 1998), CA is involved in regulating acid-base equilibrium. Its action on the renal tubules produces a mild metabolic acidosis by increasing bicarbonate excretion, which increases pulmonary ventilation. The inhibition of this enzyme by acetazolamide is used as a prophylactic treatment for acute mountain sickness (Cain and Dunn, 1966; Hackett and Rennie, 1976; Johnson and Rock, 1998). It is known that this substance produces an elevation of the arterial PO2 during acute exposure to hypoxia (Cain and Dunn, 1966). In the lungs, red cell CA is responsible for the dehydration of H2CO3 and its hydration in the tissues. Without a catalyst, the interconversion between CO2 and H2CO3 requires more than 1 minute for completion, while the capillary transit of red cells takes 1 second. The acceleration of these reactions between 13000 and 25000 fold is achieved by red cell CA (Geers and Gros, 2000). Our concern was to evaluate the activity of this enzyme in high altitude and sea level natives because there was no information available with respect to the effects of chronic hypobaric hypoxia on the CA activity of red blood cells and its relation to polycythemia. Red cell levels in patients with secondary polycythemia, as opposed to hypobaric hypoxia, were similar to the normal subjects (Funakoshi and Deutsch, 1971). It is expected that an increased production of red cell CA occurs during hypobaric hypoxia as it does with hemoglobin. This information may be useful in future attempts to treat excessive polycythemia with acetazolamide.

Blood was collected from fifteen healthy native subjects of Cerro de Pasco (4300 m) and another twelve natives of Lima (130 m). The blood was centrifuged to separate the red cell fraction, and the red cells were diluted 1/400 (v/v). The carbonic anhydrase activity was measured using the changing pH technique with a barbital buffer, a continuous flow of CO2 and the addition of increasing amounts of diluted red cells as described by Maren (1960). Units were expressed per milliliter of red cells (U/ml).

The hematocrit was measured by the microhematocrit method. Student's t test was used to compare the means between groups. Data were analyzed by SPSS for Windows v7.5, using p<0.05 for statistical significance.

Results are shown in Table I There was no correlation between hematocrit and CA activity when expressed by red cell volume. At high altitudes there is an increase of the blood volume, primarily due to an increase in the red cell fraction, otherwise the plasma volume is contracted (Sánchez et al, 1970). Blood flow at high altitude and sea level is similar (Winslow and Monge, 1987). This study showed no difference in the carbonic anhydrase activity per milliliter of red cells. However, due to the intraerythrocytic location of this enzyme, the circulating CA activity of red cells is increased, as occurs with the mass of circulating hemoglobin.

High altitude natives have a low CO2 tension and a low arterial HCO3- level (Monge et al, 1964), which is the result of their greater ventilation. However, the role of CA in this acid base equilibrium at high altitudes is unknown. CA inhibitors such as acetazolamide have been used in the treatment of many diseases, including acute mountain sickness and sleep apnea syndrome (Swenson, 1998). Chronic Mountain Sickness (CMS) is a disabling disease suffered by high altitude natives and is characterized by an excessive hypoxemia and erythrocytosis and a variety of symptoms related to the nervous system (Winslow and Monge, 1987). An attempt to treat this disease with acetazolamide required the knowledge of CA activity in the blood of those patients and was a stimulus to undertake this research. Also, blood letting used in the treatment of CMS with significant acute reduction of polycythemia could be an important experimental and clinical tools for assessing the role of CA in excessive polycythemia.

Table I

Age, hematocrit, and carbonic anhydrase activity in healthy subjects in Cerro de Pasco
(4300m) and Lima (150 m)


Lima
Cerro de Pasco
p
(n=12)
(n=15)

Age

45.3 ± 11.9
36.5 ± 13.6
0.09

Hematocrit

41.8 ± 4.7
53.0 ± 7.9
0.0002

Carbonic anhydrase activity

U/ml x 103

22.35 ± 3.9

22.93 ± 4.2
0.71

x ± s.d.

Corresponding Author: Carlos Monge-C. Universidad Peruana Cayetano Heredia. Apartado 4314, Lima 100, Perú Email: cmonge@upch.edu.pe

Received: 14, 2000. Revised: uly 21, 2000 Accepted: July 27, 2000

REFERENCES

Cain SM, Dunn JE (1966) Low doses of acetazolamide to aid accommodation of men to altitude. J Appl Physiol 21: 1195-12002        [ Links ]

Funakoshi S, Deutsch HF (1971) Human carbonic anhydrases. Levels in erythrocytes in various states. J Lab Clin Med 77: 39-45        [ Links ]

Geers C, Gros G (2000) Carbon dioxide transport and carbonic anhydrase in blood and muscle. Physiol Rev 80: 681-715        [ Links ]

Hackett PH, Rennie D (1976) The incidence, importance and prophylaxis of acute mountain sickness. Lancet 7996: 1149-1155        [ Links ]

Iturriaga R (1993) Carotid body chemoreception: The importance of CO2 _ HCO3- and carbonic anhydrase (Review). Biol Res 26: 319-329        [ Links ]

Johnson TS, Rock PB (1988) Current concepts, acute mountain sickness. NEJM 319: 841-845        [ Links ]

Maren TH (1960) A simplified micromethod for the determination of carbonic anhydrase and its inhibition. J Phar Exp Ther 130: 26-29        [ Links ]

Monge-C C, Lozano R, CarcelEn A (1964) Renal excretion of bicarbonate in high altitude natives and in natives with chronic mountain sickness. J Clin Invest 43: 2303-2309        [ Links ]

Sanchez C, Merino C, Figallo M (1970) Simultaneous measurement of plasma and cell mass in polycythemia of high altitude. J Appl Physiol 28: 775-778        [ Links ]

Swenson ER (1998) Carbonic anhydrase inhibitors and ventilation: a complex interplay of stimulation and suppression. Eur Respir J 12: 1242-1247        [ Links ]

Winslow RM, Monge CC (1987) Hypoxia, polycythemia and chronic mountain sickness. Baltimore: Johns Hopkins Press.         [ Links ]

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License