Role of calcium and other trace elements in the gastrointestinal physiology

Figure 1 Simplified model of the parietal cell showing the current mechanisms involved in acid secretion in comparison to a resting cell. The Ca²⁺-sensing receptor (CaSR) and the histamine receptor are located on the basolateral membrane. HCl secretion is mediated by H⁺ extrusion via the H⁺,K⁺-ATPase coupled with Cl^- secretion via an apical channel. Activation of the CaSR causes acid secretion via the H⁺, K⁺-ATPase.

Figure 2 Schematic of acid secretion. A: Classically defined pathway of acid secretion: Gastrin released from the G cell binds to receptors on the ECL cell causing histamine release from the ECL cell. The histamine binds to receptors on the parietal cell and stimulates proton efflux; B: Modified model of acid secretion involving a functional CaSR on the basolateral membrane of both the G cell and parietal cell. Acid secretion can be activated directly by the CaSR on the parietal cell or via the G cell pathway.

Figure 3 Cell model of proximal and distal colon. Shown are the known transport proteins in absence or presence of mineralocorticoid stimulation and their known inhibitors.

Figure 4 Current theory of roles for the Ca²⁺-sensing receptor (CaSR) in the gastrointestinal tract.