Extracellular and intracellular acid‐base regulation in crustaceans

Abstract

This article attempts to review mechanisms of intra-(ICF) and extracellular fluid (ECF) acid-base balance and the contribution each makes to whole animal acid-base homeostasis in an evolutionary progression of crustaceans (marine, freshwater, semi-and fully terrestrial). ICF pH (pHi) is regulated to preserve the functional integrity of enzymes involved in cell metabolism. The ECF is the intermediary between cellular acidhase production and whole animal exchange at the primary epithelia, the gills, and antennal gland. In vivo regulation of pHi is discussed under selected environmental conditions. Compensatory mechanisms include intracellular buffering and transmembrane exchange of acidichase equivalents including primarily an Na +/H +/HC03 -/C1-mechanism and an Na + /H + exchanger. Acid-base values and regulation in the ECF (which may be subcompartmented in selected tissues) differ in aquatic versus terrestrial species. The latter have higher PCOz (and lower pH) associated with reduced ventilation due to the higher O2 capacitance of air. Correspondingly they can regulate ECF pH (pHe) by respiratory control of PCO,; terrestrial species also depend upon mobilization of exoskeletal CaC03 to buffer protons. In aquatic species the primary mechanism of acid-base regulation is via electroneutral ion exchangers (Na+/acidic equivalent; C1 -/basic equivalent) primarily at the branchial epithelium but also apparent in the renal tubule in species that produce dilute urine (hyperosmo/ionoregulators). Evidence is presented for dynamic regulation of unidirectional branchial and renal ion fluxes for purposes of acid-base regulation. Quantitatively the antennal gland typically contributes only 10% of the overall response. Stoichiometrically, whole animal acidichasic equivalents exchanged at these epithelia originate predominantly in the ICF compartment (50-95%). Future perspectives emphasize the need to better understand how pH compensation or in some cases tolerance is related to cellular function. o 1992 Wiley-Liss, Inc.Acid-base status is an important physiological parameter in all biological fluids. In crustaceans, intracellular fluid (ICF) acid base state will affect the functional properties of proteins (i.e., enzymes) and thus cell metabolism. Extracellular fluid (ECF) acid-base state will affect the function of respiratory proteins. This fluid also acts as an intermediary between the cells, where acid-base equivalents are produced, and the external epithelia, where whole animal exchange can occur. Descriptional accounts of ECF acid-base balance have been previously published (Truchot, '83, '87; Cameron, '86). Acid-base balance is a complex phenomenon involving the interaction of a number of physiological and biochemical processes such as respiratory gas exchange, ion transport, and intermediary metabolism. These interactions were discussed recently for marine crabs (Henry and Wheatly, '92). The emphasis of the present review is an integrated, mechanistic approach to the study of whole animal acid-base balance. Intr...

The assessment of the habitat and water quality requirements of the stone crayfish (Austropotamobius torrentium) and noble crayfish (Astacus astacus) species in the rivers from the Anina Mountains (SW Romania)

“…The significant correlation with the dissolved oxygen and implicitly the negative correlations with its deficit, are underlining once again the preference of both species for a pristine environment, with a possible certain degree of toleration to organic pollution, but only up to a moderate scale (indicated as well by the degree of sites overlapping in the PCA ordination plot near the origin). Prolonged periods of hypoxia (although not registered in our study, but possible during summer time when the river is characterized by a minimum base flow), as revealed by , induce an increase in the haemolymph concentration of calcium, as a possible buffer of the acid-base variations that do occur, with an additional possible threat, being the dissolution of calcium carbonate from the exoskeleton (Truchot, 1979;Wheatly and Henry, 1992). Therefore, the short term adaptation to lower oxygen conditions (as those registered downstream the urban/rural sites) produces an increase of blood pH and calcium concentrations, resulting in an increase of the haemocyanin affinity for oxygen (Mangum, 1980).…”

Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification

“…The initial alkalization of fertilized sea urchin eggs has been hypothesized to be one of several signals inducing protein synthesis and cell functionality (32,33). pH i values for marine invertebrates were reported to range from 6.9 to 7.4 depending on species and methods used (34)(35)(36)(37)(38). The 20 mM NH 3 /NH 4 + solution induced an intracellular alkalinization leading to an increase of pH i by ∼0.2 ratio units corresponding to a ΔpH of 0.7.…”

Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

“…Affected processes include calcification, but also acid-base regulation and metabolism, growth and reproduction (Melzner et al 2009). It is known that elevated seawater PCO 2 leads to decreasing extracellular pH in crustaceans (Cameron 1978;Wheatly and Henry 1992;Pane and Barry 2007). There is also evidence that an uncompensated drop in extracellular pH has a depressing effect on aerobic energy metabolism of some tissues like muscle (Reipschläger and Pörtner 1996) and isolated liver cells (Langenbuch and Pörtner 2003), through effects on the mode and rate of proton equivalent ion exchange (Pörtner et al 2000) and a decrease in protein synthesis (Langenbuch et al 2006).…”