Gas exchange, ionoregulation and acid-base balance in fish; their interactions and the evolution of complex physiological systems.

我的长期研究目标仍然是了解鱼类（占所有脊椎动物的一半）在环境适应/适应和发育过程中气体交换，离子调节和酸碱平衡之间的相互作用。在本提案中，我将研究三个方面：1)硬鱼（占所有鱼类的95%）具有对pH非常敏感的血红蛋白（根效应），其中在特殊结构中pH值的降低大大增强了对眼睛和鳔的氧气输送，这被认为与硬鱼广泛的适应性辐射有关。然而，我们已经发现了一种机制，在根效应和血浆可达碳酸酐酶（CA）的存在下，轻微的酸碱干扰可以使组织氧卸载加倍甚至三倍。我们将进一步研究这一系统的机制，它在物种中的普遍性及其对动物生产性能的功能意义。2)虽然鳃是鱼类调节血液pH值的主要部位，但在高二氧化碳水平下，它们的这种能力受到限制。能够耐受高二氧化碳的鱼类似乎放弃了血液pH调节，而是完全保护重要组织的pHi，这与其他脊椎动物的模式根本不同，我们称之为优先pHi调节。我们将研究优先pHi调节的细胞机制，并研究一种假设，即它是脊椎动物的一种胚胎特征，在许多鱼类中保留（我们认为这代表了鱼类对空气呼吸的一种排斥），但在其他成年脊椎动物中丢失。3)一般认为脊椎动物鳃的进化主要是为了促进气体交换，其次是其他过程，如离子调节、酸碱平衡和氨排泄。然而，我们已经证明，在虹鳟鱼和七鳃鱼的早期发育过程中，早在气体交换之前，鳃就在离子调节中起主导作用。我们将描述基础发育鱼类（鲟鱼和七鳃鳗）、基础脊索动物（文昌鱼和幼被囊动物）和原脊索动物（松子虫）在休息和挑战气体交换环境（缺氧和温度）下的鳃功能。离子调节（改变水离子水平）和酸碱挑战（提高水CO2），以揭示鳃功能的可塑性，并为脊索动物鳃的生理（非摄食）作用的早期进化提供潜在的见解。拟建的实验是跨学科的，涵盖了分子、细胞和整个动物的范围。它们的目的是测试新的假设，研究结果将大大增加我们对复杂生理系统进化的理解。这三个领域都有可能改变教科书的教条。该项目将培养1名博士生、5名博士、5名硕士和15名本科生。

The long-term goal of my research program remains to understand the interaction between gas-exchange, ion regulation and acid-base balance in fish (that represent half of all vertebrates) during environmental acclimation/adaptation and development. In this proposal I will investigate three areas: 1) Teleosts (95% of all fishes) possess a very pH-sensitive hemoglobin (Root effect), where a reduction in pH in specialized structures greatly enhances O2 delivery to the eye and swimbladder which is thought to be associated with the extensive adaptive radiation of teleosts. However, we have discovered a mechanism where a mild acid-base disturbance in the presence of a Root effect and plasma accessible carbonic anhydrase (CA) can double or even triple tissue O2 unloading. We will further investigate the mechanisms involved to permit this system, it's ubiquity among species and its functional significance on whole animal performance. 2) While the gills are the primary site for blood pH regulation in fish, they become limited in this capacity at high CO2 levels. Fish that can tolerate high CO2 appear to abandon blood pH regulation and instead completely defend pHi of important tissues, a fundamentally different pattern from other vertebrates which we have termed preferential pHi (ppHi) regulation. We will investigate the cellular mechanisms for preferential pHi regulation and investigate the hypothesis that it is an embryonic trait in vertebrates that was retained in many fish species (which we propose represents an exaptation for air-breathing in fish) but lost in other adult vertebrates. 3) The vertebrate gill is generally thought to have evolved primarily to enhance gas exchange and secondarily for other processes, such as ionoregulation, acid-base balance and ammonia excretion. However, we have shown that during early development in rainbow trout and lamprey, the gills take on a dominant role for ionoregulation long before gas exchange. We will characterize gill function in basal developing fishes (sturgeon and lamprey), basal chordates (amphioxus and larval tunicates) and a protochordate (acorn worm) at rest and in environments that challenge gas exchange (hypoxia and temperature), ionoregulation (altered water ion levels) and acid-base challenges (elevated water CO2) to shed insight on the plasticity of gill function and provide potential insight into the early evolution of the physiological (non-feeding) role of the chordate gill. The proposed experiments are interdisciplinary, spanning the range of molecular, cellular, and whole animal. They are designed to test novel hypotheses and findings will add significantly to our understanding of the evolution of complex physiological systems. All 3 areas have the potential to alter textbook dogma. Overall this program will train 1 PDF, 5 Ph D, 5 MSc students and 15 undergraduate students.