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The binding of acetylcholine, gastrin and histamine
to the receptors, is a very strong stimulus for acid production. Acetylcholine
and gastrin increase the intracellular calcium concentration - calcium
is neccessary for acid production. Histamine, activates the enyme
adenyl cyclase that in turn increases the production of cyclic AMP.
Single stimulation by low levels of the 3 compounds, result in a slight
increase in acid production, but if the 3 compounds are present concurrently
even in low amounts, the acid production increases substantially.
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Within the parietal cell, water reacts with carbon
dioxide to form hydrogen and bicarbonate ions. This reaction is cataylzed
by carbonic anhydrase.
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Bicarbonate is transported out of the basolateral
membrane in exchange for chloride.
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Potassium and chloride ions diffuse into the lumen.
A hydrogen ion binds on the internal side of the hydrogen/potassium
pump, whilst a potassium ion binds to the external side. In the presence
of ATP, the pump undergoes a conformational change, and potassium
is released inside while hydrogen is released in the lumen.
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