Nellans H N, Goldsmith R S
Am J Physiol. 1981 Jun;240(6):G424-31. doi: 10.1152/ajpgi.1981.240.6.G424.
Transepithelial calcium transport has been investigated in rat cecum under in vitro voltage-clamp conditions. Under short-circuit conditions, the cecum behaves as a relatively tight epithelium for calcium fluxes, where mucosal-to-serosal (JCam leads to s) flux exceeds the reverse flux by at least 15-fold. JCanet is abolished in the presence of 1 mM N-ethylmaleimide, is inhibited by 40% with 1 mM ouabain, and is decreased by at least 60% when medium sodium is replaced by choline. Voltage-clamping experiments suggest that both electroneutral- and electrogenic-mediated calcium fluxes traverse the cell in the mucosal-to-serosal direction. Serosal-to-mucosal flux is purely diffusional and probably constrained to the paracellular pathway. In rats weighing less than 175 g, a low-calcium diet has no significant stimulatory effect on JCam leads to s, but a high-calcium diet markedly reduces this flux. These results suggest that the cecum possesses the highest density of calcium transport sites in the rat intestine and is ideally suited for bulk calcium absorption, which may be "down regulated" in response to an increased calcium load in growing animals.
在体外电压钳制条件下，对大鼠盲肠的跨上皮钙转运进行了研究。在短路条件下，盲肠对于钙通量而言表现为相对紧密的上皮组织，其中黏膜到浆膜（JCam导致s）的通量比反向通量至少高15倍。JCanet在1 mM N - 乙基马来酰亚胺存在时被消除，在1 mM哇巴因作用下被抑制40%，当培养基中的钠被胆碱替代时至少降低60%。电压钳制实验表明，电中性介导和生电介导的钙通量均沿黏膜到浆膜方向穿过细胞。浆膜到黏膜的通量纯粹是扩散性的，可能局限于细胞旁途径。在体重小于175 g的大鼠中，低钙饮食对JCam导致s没有显著的刺激作用，但高钙饮食会显著降低这种通量。这些结果表明，盲肠在大鼠肠道中具有最高密度的钙转运位点，非常适合大量钙的吸收，而在生长动物中，随着钙负荷的增加，这种吸收可能会被“下调”。
