Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada.
Comp Biochem Physiol A Mol Integr Physiol. 2010 Apr;155(4):493-502. doi: 10.1016/j.cbpa.2009.09.020. Epub 2009 Sep 25.
The present study reports aspects of GI tract physiology in the white-spotted bamboo shark, Chiloscyllium plagiosum, little skate, Leucoraja erinacea and the clear nose skate, Raja eglanteria. Plasma and stomach fluid osmolality and solute values were comparable between species, and stomach pH was low in all species (2.2 to 3.4) suggesting these elasmobranchs may maintain a consistently low stomach pH. Intestinal osmolality, pH and ion values were comparable between species, however, some differences in ion values were observed. In particular Ca(2+) (19.67+/-3.65mM) and Mg(2+) (43.99+/-5.11mM) were high in L. erinacea and Mg(2+) was high (130.0+/-39.8mM) in C. palgiosum which may be an indication of drinking. Furthermore, intestinal fluid HCO(3)(-) values were low (8.19+/-2.42 and 8.63+/-1.48mM) in both skates but very high in C. plagiosum (73.3+/-16.3mM) suggesting ingested seawater may be processed by species-specific mechanisms. Urea values from the intestine to the colon dropped precipitously in all species, with the greatest decrease seen in C. plagiosum (426.0+/-8.1 to 0mM). This led to the examination of the molecular expression of both a urea transporter and a Rhesus like ammonia transporter in the intestine, rectal gland and kidney in L. erinacea. Both these transporters were expressed in all tissues; however, expression levels of the Rhesus like ammonia transporter were orders of magnitude higher than the urea transporter in the same tissue. Intestinal flux rates of solutes in L. erinacea were, for the most part, in an inward direction with the notable exception of urea. Colon flux rates of solutes in L. erinacea were all in an outward direction, although absolute rates were considerably lower than the intestine, suggestive of a much tighter epithelia. Results are discussed in the context of the potential role of the GI tract in salt and water, and nitrogen, homeostasis in elasmobranchs.
本研究报告了白斑竹鲨、Leucoraja erinacea 小鳐鱼和 Raja eglanteria 透明鼻鳐鱼的消化道生理学的各个方面。种间血浆和胃液渗透压和溶质值相当，且所有种的胃 pH 值均较低（2.2 至 3.4），表明这些软骨鱼类可能保持一致的低胃 pH 值。种间的肠渗透压、pH 值和离子值相当，但观察到一些离子值存在差异。特别是 L. erinacea 的 Ca(2+)（19.67+/-3.65mM）和 Mg(2+)（43.99+/-5.11mM）较高，C. palgiosum 的 Mg(2+)（130.0+/-39.8mM）较高，这可能表明它们有饮水行为。此外，两种鳐鱼的肠液 HCO(3)(-)值较低（8.19+/-2.42 和 8.63+/-1.48mM），但 C. plagiosum 的 HCO(3)(-)值非常高（73.3+/-16.3mM），这表明摄入的海水可能通过特定于物种的机制进行处理。所有种的肠到结肠的尿素值急剧下降，C. plagiosum 的下降幅度最大（426.0+/-8.1 至 0mM）。这导致了对 L. erinacea 肠、直肠腺和肾脏中尿素转运体和 Rh 氨转运体的分子表达进行了检查。这两种转运体在所有组织中均有表达；然而，在同一组织中，Rh 氨转运体的表达水平比尿素转运体高出几个数量级。L. erinacea 中溶质的肠内通量大多是向内的，只有尿素是例外。L. erinacea 结肠中溶质的通量均为向外，尽管绝对速率远低于肠内，提示上皮组织紧密得多。结果在软骨鱼类盐和水以及氮体内平衡中，胃肠道的潜在作用的背景下进行了讨论。
