Karbach U, Rummel W
Naunyn Schmiedebergs Arch Pharmacol. 1987 Jan;335(1):91-6. doi: 10.1007/BF00165042.
Concentration dependence of strontium (Sr) fluxes across the colon ascendens and descendens of the rat were measured in a modified Ussing-chamber. Mucosa (m) to serosa (s) and s to m Sr fluxes across both colonic segments were linearly related to the Sr concentration from 0.125 mmol/l to 10 mmol/l. In the colon ascendens m to s Sr fluxes were slightly higher than the fluxes in the opposite direction, resulting in net Sr absorption. In the colon descendens s to m fluxes were higher than the ms fluxes, resulting in net Sr secretion. Neither Sr nor calcium (Ca) showed a concentration dependent interaction with respect to their unidirectional fluxes in both parts of the colon. Only in the colon ascendens Sr at the highest concentration (10 mmol/l) inhibited m to s calcium transport. Experiments, in which the voltage dependence of the unidirectional Sr fluxes was measured confirmed the results obtained from the concentration dependence: The unidirectional fluxes of Sr across the colon ascendens and descendens were totally voltage dependent, i.e. diffusive. In the colon descendens the voltage dependence of the s to m flux was steeper than the flux from m to s. It is hypothesized that this prevalence is caused by an anomalous solvent drag effect. 1.25-Dihydroxyvitamin D3 [1.25 (OH)2D3] stimulated m to s calcium flux in the colon descendens but had no effect on Sr flux. The results demonstrate that Sr and Ca in the rat colon are transported by different mechanisms. In contrast to the Ca transport the Sr flux is only diffusive and insensitive to 1.25 (OH)2D3.
在改良的尤斯灌流小室中测量了锶（Sr）跨大鼠升结肠和降结肠的通量的浓度依赖性。在0.125 mmol/l至10 mmol/l的Sr浓度范围内，跨两个结肠段的黏膜（m）到浆膜（s）以及s到m的Sr通量与Sr浓度呈线性关系。在升结肠中，m到s的Sr通量略高于相反方向的通量，导致Sr的净吸收。在降结肠中，s到m的通量高于m到s的通量，导致Sr的净分泌。在结肠的两个部分中，Sr和钙（Ca）在其单向通量方面均未表现出浓度依赖性相互作用。仅在升结肠中，最高浓度（10 mmol/l）的Sr抑制了m到s的钙转运。测量单向Sr通量的电压依赖性的实验证实了从浓度依赖性获得的结果：Sr跨升结肠和降结肠的单向通量完全依赖于电压，即扩散性的。在降结肠中，s到m通量的电压依赖性比m到s的通量更陡峭。据推测，这种优势是由异常溶剂拖曳效应引起的。1,25 - 二羟基维生素D3 [1,25(OH)2D3]刺激了降结肠中m到s的钙通量，但对Sr通量没有影响。结果表明，大鼠结肠中的Sr和Ca通过不同机制转运。与Ca转运不同，Sr通量仅是扩散性的，并且对1,25(OH)2D3不敏感。
