Parietal cells determination

A drug may also be used to diagnose a disease. Histamine has been used to assess the ability of the stomach to secrete acid and to determine parietal cell mass. If an acidity or hyposecretion... 

I. Marks, Wilfred Card (191) Use of HA test to determine parietal cell mass... 

The last mediator of gastric secretion in the parietal cell is an H+,K+-ATPase (proton or acid pump) which is a member of the phosphorylating class of ion transport ATPases. Hydrolysis of ATP results in ion transport. This chemical reaction induces a conformational change in the protein that allows an electroneutral exchange of cytoplasmic H+ for K+. The pump is activated when associated with a potassium chloride pathway in the canalicular membrane which allows potassium chloride efflux into the extracytoplasmic space, and thus results in secretion of hydrochloric acid at the expense of ATP breakdown. The activity of the pump is determined by the access of K+ on this surface on the pump. In the absence of K+, the cycle stops at the level of the phosphoenzyme [137]. 

When Torsten Teorell made his thesis at the Karolinska Institute in Stockholm in 1933, he presented an alternative explanation of the variations in composition with rate of secretion his back-diffusion theory. Teorell refined and elaborated his theory in 1947, " and after he became professor of physiology at Uppsala, his students, notably Karl Johann Obrink, provided further evidence supporting it. Teorell said that HCl is secreted by the parietal cells at some yet to be determined primary concentration. At or near the site of secretion, HCl diffuses through a permeable barrier in exchange for NaCl from plasma. Tick s equation applies to the diffusion process, and HCl and NaCL diffuse as ion pairs. No diluting or neutralizing fluid is secreted. Teorell, who was much more interested in physical... 

McDogual [sic] WS, DeCosse JJ. Method for determining differential secretory function of isolated cells in vitro Chloride movement in isolated parietal cells. Exp Cell Res 61 203-206, 1970. 

Acid secretion is a regulated process whose rate is determined by its necessity after a meal. Consequently, the eventual result of the complex mechanisms for regulation of secretion described in previous sections is to activate the H,K ATPase. In contrast to the regulation of many other enzymes, there is no evidence for any chemical factors that directly influence the activity of the H,K ATPase, other than the availability of the necessary substrates MgATP, H, and K. Because within the parietal cell the availability of protons and AAgATP is not likely to be rate limiting, it follows that the major, if not the only, factor that controls proton transport is the availability of K at the extracytosolic surface of the H,K ATPase. Substantial evidence has accumulated to indicate that this is indeed the case, and that activation of the proton pump results from association of the H,K ATPase with a K and Cl" permeability in the membrane of the secretory canaliculus. 

The two subunits of the ATPase are synthesized In the ER of the parietal cell. The only other location of the pump Is In the Intercalated cells of the collecting duct of the kidney. Formation of transmembrane segments requires Interaction of hydrophobic sequences during translation with the Interior surface of the translocon. A sequence that determines membrane Insertion with Its N-termlnal cytoplasmic and C-termlnal extracytoplasmic Is termed a s/gna/ anchor sequence. A sequence that returns the translating protein back to the cytoplasm and, thus, with Its N-termlnal extracytoplasmic, Is named a stop transfer sequence. 

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