Luminal and endocrine factors for regulation of intestinal monosaccharide and Ca2+ transport

Intestinal glucose and calcium (Ca2+) absorption as well as their respective regulatory processes have been studied in detail in different species. Regulation is mediated from the luminal and the blood side of the barrier. For increasing glucose uptake, L-type Ca2+ channels in connection with cytoskeletal rearrangement have been identified as relevant factors for the insertion of glucose transporter 2 (GLUT2) into the apical membrane. Apical located sweet taste receptors can be stimulated by high luminal glucose concentrations or artificial sweeteners which also results in stronger GLUT2 insertion. During long-term adaptation, sweet taste receptors mediate the upregulation of a sodium-dependent glucose transport system (SGLT1), which involves the activation of cAMP pathway. Therefore, it is assumed that sweet taste receptors are able to modulate short-term as well as long-term adaptation through the activation of different pathways. For endocrine regulation glucagon-like peptides, glucose-dependent insulinotropic polypeptide and leptin are under discussion. For Ca2+ para- and transcellular pathways contribute to Ca2+ absorption which includes transient receptor potential channels (TRP). Controversy still exists on the essential role of calbindin-D9k for cellular transfer of Ca2+. Calcitriol, Ca2+ itself and other nutritional factors such as carbohydrates and short-chain fatty acids are involved in regulation of intestinal Ca2+ absorption.