Maddrell S H, Whittembury G, Mooney R L, Harrison J B, Overton J A, Rodriguez B
Department of Zoology, Cambridge, UK.
J Exp Biol. 1991 May;157:483-502. doi: 10.1242/jeb.157.1.483.
We have investigated the fate of the large amounts of calcium ingested by Rhodnius prolixus in its meals of blood. 45Ca2+ injected into the haemolymph or fed to fifth-stage Rhodnius reared on rabbits is accumulated at high concentrations in the cells of the upper Malpighian tubules; very little is excreted from the body This 45Ca2+ accumulation goes on continuously for at least 12 days and the rate of uptake is increased several-fold within 3-4 days of a meal. The extent of calcium accumulation in tubule cells is correlated with the presence of intracellular membrane-bound concretion bodies, which are therefore likely sites of calcium deposition. X-ray diffraction showed that the calcium deposits are non-crystalline. Tubules from rabbit-fed fifth-stage Rhodnius contain 410 mmol l-1 calcium; in those from chicken-fed insects the calcium concentration is over 1 mol l-1; and in those fed in vitro on heparinised low-K+ sheep blood the calcium concentration is only 21 mmol l-1. The concentration of calcium in the haemolymph in all these insects was 8 mmol l-1 and its activity determined by an ion-selective electrode was 2.5 mmol l-1. 45Ca2+ deposited in the tubules is readily exchangeable, but the efflux preferentially passes to the haemolymph side of the tubule epithelium. The ability to sequester calcium in the Malpighian tubules may prevent calcium from interfering with reabsorptive processes in the rectum.
我们研究了吸血猎蝽（Rhodnius prolixus）在吸食血液时摄入的大量钙的去向。将45Ca2+注入血淋巴或喂给以兔子为食的五龄猎蝽，其在上部马氏管细胞中大量积累；很少从体内排出。这种45Ca2+的积累至少持续12天，并且在进食后的3 - 4天内摄取速率增加了几倍。马氏管细胞中钙的积累程度与细胞内膜结合的结石体的存在相关，因此结石体可能是钙沉积的部位。X射线衍射显示钙沉积物是非晶态的。以兔子为食的五龄猎蝽的马氏管中钙含量为410 mmol l-1；以鸡为食的昆虫的马氏管中钙浓度超过1 mol l-1；而在体外以肝素化低K+羊血为食的昆虫的马氏管中钙浓度仅为21 mmol l-1。所有这些昆虫血淋巴中的钙浓度均为8 mmol l-1，用离子选择性电极测定其活性为2.5 mmol l-1。沉积在马氏管中的45Ca2+很容易交换，但外流优先流向马氏管上皮的血淋巴侧。马氏管中螯合钙的能力可能会阻止钙干扰直肠中的重吸收过程。
