Nathanson M H, Mariwalla K
Center for Membrane Toxicity Studies, Mount Desert Island Biological Laboratory, Salsbury Cove, Maine 04672, USA.
Am J Physiol. 1996 Mar;270(3 Pt 2):R561-70. doi: 10.1152/ajpregu.1996.270.3.R561.
Hormonal regulation of hepatocytes, via cytosolic Ca2+ signaling, is well established in higher life forms but has not been investigated in elasmobranchs. We therefore examined Ca2+ signaling in hepatocytes isolated from the little skate, Raja erinacea. In hepatocyte populations, ATP induced a rapid, biphasic increase in Ca2+, as it does in mammalian hepatocytes. Other hormones that act on mammalian hepatocytes, such as vasopressin, angiotensin, and phenylephrine, induced no such Ca2+ increase. The initial phase of the ATP-induced Ca2+ increase was seen even in Ca(2+)-free medium, whereas the late sustained phase of the increase was not. Similar dose-response curves were obtained by stimulation with ATP, ADP, UTP, and 2-methylthio-ATP. In contrast, AMP, adenosine, beta, gamma-methyl-ATP, CTP, and GTP induced little or no Ca2+ increase. In single hepatocytes, ATP, ADP, UTP, and 2-methylthio-ATP each induced a sustained increase in Ca2+ at high concentrations, but at low concentrations induced Ca2+ oscillations. A maximal concentration of ATP (100 microM) caused a marked, transient increase in bile flow in the isolated perfused skate liver, whereas 100 microM adenosine had no such effect. These findings demonstrate that skate hepatocytes possess P2 nucleotide receptors that link to intracellular plus extracellular Ca2+ mobilization, which in turn regulates bile secretion. The broad specificity of the response to ATP and related compounds suggests either that multiple types of P2 receptors are expressed by skate hepatocytes or else that these cells possess a single primitive nucleotide receptor from which other P2 subtypes subsequently evolved.
在高等生物中，通过胞质Ca2+信号传导对肝细胞进行激素调节已得到充分证实，但在板鳃亚纲鱼类中尚未进行研究。因此，我们检测了从小眼鳐（Raja erinacea）分离的肝细胞中的Ca2+信号传导。在肝细胞群体中，ATP诱导Ca2+快速双相增加，这与哺乳动物肝细胞中的情况相同。其他作用于哺乳动物肝细胞的激素，如血管加压素、血管紧张素和去氧肾上腺素，并未诱导这种Ca2+增加。即使在无Ca(2+)的培养基中也能观察到ATP诱导的Ca2+增加的初始阶段，而增加的后期持续阶段则未观察到。用ATP、ADP、UTP和2-甲硫基-ATP刺激可获得相似的剂量反应曲线。相比之下，AMP、腺苷、β,γ-甲基-ATP、CTP和GTP诱导的Ca2+增加很少或没有增加。在单个肝细胞中，ATP、ADP、UTP和2-甲硫基-ATP在高浓度时均诱导Ca2+持续增加，但在低浓度时诱导Ca2+振荡。ATP的最大浓度（100 microM）导致离体灌注鳐肝胆汁流量显著短暂增加，而100 microM腺苷则无此作用。这些发现表明，鳐肝细胞具有与细胞内和细胞外Ca2+动员相关的P2核苷酸受体，进而调节胆汁分泌。对ATP和相关化合物反应的广泛特异性表明，要么鳐肝细胞表达多种类型的P2受体，要么这些细胞拥有单一的原始核苷酸受体，其他P2亚型随后从该受体进化而来。
