Pedrozo H A, Schwartz Z, Luther M, Dean D D, Boyan B D, Wiederhold M L
Department of Physiology, University of Texas Health Science Center at San Antonio 78284, USA.
Hear Res. 1996 Dec 1;102(1-2):51-62. doi: 10.1016/s0378-5955(96)00147-5.
The gravity-sensing organ of Aplysia californica consists of bilaterally paired statocysts containing statoconia, which are granules composed of calcium carbonate crystals in an organic matrix. In early embryonic development, Aplysia contain a single granule called a statolith, and as the animal matures, statoconia production takes place. The objective of this study was to determine the effect of hypergravity on statoconia production and homeostasis and explore a possible physiologic mechanism for regulating this process. Embryonic Aplysia were exposed to normogravity or 3 x g or 5.7 x g and each day samples were analyzed for changes in statocyst, statolith, and body dimensions until they hatched. In addition, early metamorphosed Aplysia (developmental stages 7-10) were exposed to hypergravity (2 x g) for 3 weeks, and statoconia number and statocyst and statoconia volumes were determined. We also determined the effects of hypergravity on statoconia production and homeostasis in statocysts isolated from developmental stage 10 Aplysia. Since prior studies demonstrated that urease was important in the regulation of statocyst pH and statoconia formation, we also evaluated the effect of hypergravity on urease activity. The results show that hypergravity decreased statolith and body diameter in embryonic Aplysia in a magnitude-dependent fashion. In early metamorphosed Aplysia, hypergravity decreased statoconia number and volume. Similarly, there was an inhibition of statoconia production and a decrease in statoconia volume in isolated statocysts exposed to hypergravity in culture. Urease activity in statocysts decreased after exposure to hypergravity and was correlated with the decrease in statoconia production observed. In short, there was a decrease in statoconia production with exposure to hypergravity both in vivo and in vitro and a decrease in urease activity. It is concluded that exposure to hypergravity downregulates urease activity, resulting in a significant decrease in the formation of statoconia.
加州海兔的重力感应器官由两侧成对的平衡囊组成，平衡囊内含有平衡石，平衡石是由碳酸钙晶体在有机基质中构成的颗粒。在胚胎发育早期，海兔含有一个称为静纤毛石的单一颗粒，随着动物的成熟，平衡石开始产生。本研究的目的是确定超重力对平衡石产生和内稳态的影响，并探索调节这一过程的可能生理机制。将胚胎期的海兔暴露于正常重力、3倍重力或5.7倍重力环境下，每天对样本进行分析，观察平衡囊、静纤毛石和身体尺寸的变化，直至它们孵化。此外，将早期变态的海兔（发育阶段7 - 10）暴露于超重力（2倍重力）环境3周，然后测定平衡石数量、平衡囊和平衡石体积。我们还确定了超重力对从发育阶段10的海兔分离出的平衡囊中平衡石产生和内稳态的影响。由于先前的研究表明脲酶在平衡囊pH值调节和平衡石形成中起重要作用，我们还评估了超重力对脲酶活性的影响。结果表明，超重力以剂量依赖的方式降低了胚胎期海兔的静纤毛石和身体直径。在早期变态的海兔中，超重力降低了平衡石数量和体积。同样，在培养中暴露于超重力的分离平衡囊中，平衡石产生受到抑制，平衡石体积减小。暴露于超重力后，平衡囊中脲酶活性降低，且与观察到的平衡石产生减少相关。简而言之，体内和体外暴露于超重力均导致平衡石产生减少以及脲酶活性降低。结论是，暴露于超重力会下调脲酶活性，导致平衡石形成显著减少。
