University of Wisconsin-Madison, Department of Forest and Wildlife Ecology, Madison, WI 53706, United States.
University of Wisconsin-Madison, Department of Forest and Wildlife Ecology, Madison, WI 53706, United States; Instituto Multidisciplinario de Investigaciones Biológicas de San Luis, Consejo Nacional de Investigaciones Científicas y Técnicas, 5700 San Luis, Argentina; Departamento de Biología, Universidad de San Luis, 5700 San Luis, Argentina.
Comp Biochem Physiol A Mol Integr Physiol. 2021 Mar;253:110860. doi: 10.1016/j.cbpa.2020.110860. Epub 2020 Dec 1.
The small intestine of mammals and birds exhibits fascinating variation across taxa, body size, and life history features such as locomotion and diet. In the intestine's brush border membrane (BBM), hydrolases are more abundant than transporters in both mammals and birds, but there are differences among the groups in abundance of certain hydrolases and possibly in transporters. For example, mammals express two α-glucosidases, sucrase-isomaltase (SI) and maltase glucoamylase (MGAM), whereas songbirds we studied have only SI, and the chicken expresses SI plus another α-glucosidase that functions similarly to MGAM but is not a true ortholog. For intestinal absorption of sugars and amino acids, small fliers rely on a paracellular pathway to a greater extent than do nonflying mammals, which rely more on transporters. Possibly having evolved in fliers as compensation for lower intestinal nominal surface area (NSA), the fliers' reliance on paracellular absorption is supported by their greater villous surface enlargement that leads to more (per cm NSA) tight junctions and greater clearance of passively absorbed compounds. To match digestive capacity to nutrient load, a positive relationship is often observed between dietary intake of macronutrients and intestinal activity of the enzymes and transporters of their respective constituents. In enterocytes, rapid, fine-tuned adjustment to high dietary carbohydrate and protein involves rapid, specific correlated increase in activity and abundance of hydrolases and transporters in the BBM and increases in their mRNA.
哺乳动物和鸟类的小肠在分类学、体型和生活史特征（如运动和饮食）方面表现出令人着迷的变化。在肠刷状缘膜（BBM）中，水解酶的丰度在哺乳动物和鸟类中都高于转运蛋白，但在某些水解酶和转运体的丰度上存在群体差异。例如，哺乳动物表达两种α-葡萄糖苷酶，蔗糖酶-异麦芽糖酶（SI）和麦芽糖酶葡糖苷酶（MGAM），而我们研究的鸣禽只有 SI，鸡则表达 SI 加上另一种α-葡萄糖苷酶，其功能类似于 MGAM，但不是真正的同源物。对于糖和氨基酸的肠道吸收，小型飞行者比非飞行哺乳动物更依赖细胞旁途径，非飞行哺乳动物更依赖转运蛋白。可能是在飞行者中进化而来，以弥补较低的肠名义表面积（NSA），飞行者对细胞旁吸收的依赖得到了它们更大的绒毛表面积扩大的支持，这导致了更多（每厘米 NSA）紧密连接和被动吸收化合物的清除。为了使消化能力与营养负荷相匹配，通常观察到膳食中宏量营养素的摄入与各自成分的酶和转运蛋白的肠道活性之间存在正相关关系。在肠细胞中，对高膳食碳水化合物和蛋白质的快速、精细调节涉及 BBM 中水解酶和转运蛋白活性和丰度的快速、特异性相关增加，以及它们的 mRNA 增加。
