Calcium,
Carbonic Anhydrase and Gastric Acid Secretion
I.
PUSCAS, M. COLTAU1, M. BAICAN2,
G. DOMUTA1, A. HECHT3
University
of Medicine Oradea, 1Romanian
Medical Academy of Sciences, Center for Research
and Medical Assistance Simleu Silvaniei, Romania,
2Clinic Wilkenberg,
Germany, 3Medical
Care Unit, New York, USA
Received
February 9, 2000
Accepted September 20, 2000
Summary
Previous
data concerning the action of calcium (Ca) on
gastric acid secretion (GAS) indicated that
calcium ions increase GAS elicited by gastrin
released through a vagal mechanism, and also by a
direct effect on parietal cells. Our research
showed that the stimulating effect of calcium on
gastric acid secretion can be antagonized by
verapamil administration, which reduces gastric
acid secretion . In the present study we followed
the effect induced by administration of calcium
and Ca-chelating agents (disodium EDTA) on
gastric acid secretion and on carbonic anhydrase
(CA) activity. We selected two groups of healthy
volunteers: Group I (n=21) received a single i.v.
dose of CaCl2 (15 mg/kg b.w.), whereas Group II
(n=22) received a single i.v. dose of disodium
EDTA (5 mg/kg b.w.). We determined blood calcium
before and after treatment, gastric acid
secretion at 2 hours, erythrocyte CA II activity,
and CA IV activity in membrane parietal cells,
which were isolated from gastric mucosa obtained
by endoscopic biopsy. Assessment of carbonic
anhydrase activity was achieved by the
stopped-flow method. In Group I calcium
administration increased blood calcium, HCl
output, CA II and CA IV activity as compared to
initial values. In Group II, disodium EDTA
reduced blood calcium, HCl output, CA II and CA
IV activity as compared to initial values. The
results demonstrated that increased blood calcium
and GAS values after calcium administration
correlated with the increase of erythrocyte CA II
and parietal cell CA IV activity, while disodium
EDTA induced a reversed process. Our results also
show that cytosolic CA II and membrane CA IV
values are sensitive to calcium changes and they
directly depend on these levels. Our data suggest
that intra- and extracellular pH changes induced
by carbonic anhydrase might account for the
modulation of the physiological and pathological
secretory processes in the organism.
Key
words
Calcium
· Disodium EDTA · Carbonic anhydrase · Gastric
acid secretion
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Prof.
Dr. Ioan Puscas, MD, Center for Research and
Medical Assistance , 4775 Simleu Silvaniei, 37
Dunarii Street, Salaj, Romania Fax +40-60-678320.
E-mail: ccam@teli.netcompsj.ro
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