Role of cytosolic carbonic anhydrase Ca17a in cardiorespiratory responses to CO2 in developing zebrafish (Danio rerio).

The sensing of environmental fluctuations and initiation of appropriate physiological responses is crucial to homeostasis. Neuroepithelial cells (NECs) in fishes are putative chemoreceptors, resembling mammalian Type I (glomus) cells, that respond in vitro to changes in O2, CO2, NH3, and pH. Cytosolic carbonic anhydrase (Ca17a) is thought to be involved in CO2 sensing owing to its presence in NECs. Zebrafish (Danio rerio) lacking functional Ca17a were generated via CRISPR/Cas9 technology and used to assess the role of Ca17a in initiating the cardiorespiratory responses to elevated CO2 (hypercapnia). Unfortunately, the homozygous knockout mutants (ca17a-/-) did not survive more than ∼12-14 days postfertilization (dpf), restricting experiments to early developmental stages (4-8 dpf). Changes in ventilation (fV) and cardiac (fH) frequency in response to hypercapnia (1% CO2) in wild-type (ca17a+/+), heterozygous (ca17a+/-) and ca17a-/- fish were used to investigate Ca17a-dependent CO2 sensing and downstream signaling. Wild-type fish exhibited hyperventilation during hypercapnia as indicated by an increase in fV. In the ca17a-/- fish, the hyperventilatory response was attenuated markedly but only at 8 dpf. Hypercapnic tachycardia was observed for all genotypes and did not appear to be influenced by the absence of Ca17a. Interestingly, ca17a-/- fish exhibited a significantly lower resting fH that became more pronounced as the fish aged. The decrease in resting fH was prevented ("rescued") when ca17a-/- embryos were injected with ca17a mRNA. Collectively, the results of this study support a role for Ca17a in promoting hyperventilation during hypercapnia in larval zebrafish and suggest a previously unrecognized role for Ca17a in determining resting heart rate.

Hypoxia tolerance decreases with body size in red drum Sciaenops ocellatus.

Mass-specific oxygen consumption rate, i.e. standard metabolic rate (Rs ) and critical oxygen tension (Pcrit ) of red drum Sciaenops ocellatus were measured and scaled over a 2500-fold range in mass (MF ; 0·26-686 g). Rs conformed to well established models (Rs = 3·73·91 MF (-0·21) ; r(2) = 0·86) while Pcrit increased over the size range (Pcrit = 3·15 log10 MF + 16·19; r(2) = 0·44). This relationship may be ecologically advantageous as it would allow smaller S. ocellatus to better utilize hypoxic zones as habitat and refuge from predators.

Improvement of corrosion and biological properties of microarc oxidized coatings on Mg-Zn-Zr alloy by optimizing negative power density parameters.

Corrosion and biological properties of microarc oxidized calcium phosphate (CaP) coatings on Mg-Zn-Zr alloy were improved by optimizing negative power density parameters. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were employed to characterize the coating morphology and phase composition. The in vitro cytotoxicity and systemic toxicity tests were carried out to evaluate the coating biocompatibility. The degradability and bioactivity of the coatings were determined by in vitro simulated body fluid (SBF) immersion test. The coating microstructure, thickness and growth rate can be influenced by negative power density through changing direction of ions movements, rate of ions exchanges and affecting formation of plasma. The CaP coatings reduced the substrate degradation rate. Calcium phosphates, such as hydroxyapatite (Ca10(PO4)6(OH)2, HA) and calcium pyrophosphate (Ca2P2O7, CPP), etc., were induced after 30 days SBF immersion, indicating that the coatings have bioactivity. The CaP coatings have no toxicity to cell and living mice, indicating that the coatings are safe to serve as implants.

Effects of phosphates on microstructure and bioactivity of micro-arc oxidized calcium phosphate coatings on Mg-Zn-Zr magnesium alloy.

Calcium phosphate (CaP) coatings were prepared on Mg-Zn-Zr magnesium alloy by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH3COO)2Ca·H2O) and different phosphates (i.e. disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), sodium phosphate (Na3PO4·H2O) and sodium hexametaphosphate((NaPO3)6)). Scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray diffractometer (XRD) were employed to characterize the microstructure, elemental distribution and phase composition of the CaP coatings. Simulated body fluid (SBF) immersion test was used to evaluate the coating bioactivity and degradability. Systemic toxicity test was used to evaluate the coating biocompatibility. Fluoride ion selective electrode (ISE) was used to measure F(-) ions concentration during 30 days SBF immersion. The CaP coatings effectively reduced the corrosion rate and the surfaces of CaP coatings were covered by a new layer formed of numerous needle-like and scale-like apatites. The formation of these calcium phosphate apatites indicates that the coatings have excellent bioactivity. The coatings formed in (NaPO3)6-containging electrolyte exhibit thicker thickness, higher adhesive strength, slower degradation rate, better apatite-inducing ability and biocompatibility.

Microstructure and biological properties of micro-arc oxidation coatings on ZK60 magnesium alloy.

Ceramic coatings were prepared on ZK60 magnesium alloy in electrolyte with different concentration ratio of calcium and phosphorus (Ca/P) by micro-arc oxidation (MAO) technique at constant voltage. The microstructure, phase composition, elemental distribution, corrosion resistance, and adhesion of the coatings were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD), energy-dispersive X-ray spectrometry (EDS), electrochemical workstation, and scratch spectrometer, respectively. The coating biocompatibility was evaluated by in vitro cytotoxicity tests and systemic toxicity tests, and the bioactivity and degradability were evaluated by simulation body fluid (SBF) immersion tests. SEM shows that pores with different shapes distribute all over the coating surface. The adhesion and thickness of the coatings increases with increasing Ca/P ratio of electrolyte. The in vitro cytotoxicity tests and systemic toxicity texts demonstrate that the coatings have no toxicity to cell and living animal, which show that the coatings have excellent biocompatibility. XRD analysis shows that bioactive calciumphosphate (CaP) phases such as hydroxyapatite (HA, Ca(10)(PO(4))(6)(OH)(2)) and calcium pyrophosphate (CPP, Ca(2)P(2)O(7)) are induced in the immersed coatings, indicating that the MAO coatings have excellent bioactivity.