Journal of Comparative Physiology B

, Volume 184, Issue 7, pp 891–902 | Cite as

Adjustments in cholinergic, adrenergic and purinergic control of cardiovascular function in snapping turtle embryos (Chelydra serpentina) incubated in chronic hypoxia

Original Paper

Abstract

Adenosine is an endogenous nucleoside that acts via G-protein coupled receptors. In vertebrates, arterial or venous adenosine injection causes a rapid and large bradycardia through atrioventricular node block, a response mediated by adenosine receptors that inhibit adenylate cyclase and decrease cyclic AMP concentration. Chronic developmental hypoxia has been shown to alter cardioregulatory mechanisms in reptile embryos, but adenosine’s role in mediating these responses is not known. We incubated snapping turtle embryos under chronic normoxic (N21; 21 % O2) or chronic hypoxic conditions (H10; 10 % O2) beginning at 20 % of embryonic incubation. H10 embryos at 90 % of incubation were hypotensive relative to N21 embryos in both normoxic and hypoxic conditions. Hypoxia caused a hypotensive bradycardia in both N21 and H10 embryos during the initial 30 min of exposure; however, fH and Pm both trended towards increasing during the subsequent 30 min, and H10 embryos were tachycardic relative to N21 embryos in hypoxia. Following serial ≥1 h exposure to normoxic and hypoxic conditions, a single injection of adenosine (1 mg kg−1) was given. N21 and H10 embryos responded to adenosine injection with a rapid and large hypotensive bradycardia in both normoxia and hypoxia. Gene expression for adenosine receptors were quantified in cardiac tissue, and Adora1 mRNA was the predominant receptor subtype with transcript levels 30–82-fold higher than Adora2A or Adora2B. At 70 % of incubation, H10 embryos had lower Adora1 and Adora2B expression compared to N21 embryos. Expression of Adora1 and Adora2B decreased in N21 embryos during development and did not differ from H10 embryos at 90 % of incubation. Similar to previous results in normoxia, H10 embryos in hypoxia were chronically tachycardic compared to N21 embryos before and after complete cholinergic and adrenergic blockade. Chronic hypoxia altered the development of normal cholinergic and adrenergic tone, as well as adenosine receptor mRNA levels. This study demonstrates that adenosine may be a major regulator of heart rate in developing snapping turtle embryos, and that chronic hypoxic incubation alters the response to hypoxic exposure.

Keywords

Embryo Fetus Hypoxia Reptile Gene expression 

Abbreviations

CAM

Chorioallantoic membrane

fH

Heart rate (beats min−1), ‘frequency of heart beats’

H10

Turtle embryos artificially incubated in chronic hypoxia (10 % O2), beginning at 20 % of incubation/development

N21

Turtle embryos artificially incubated in chronic normoxia (21 % O2), beginning at 20 % of incubation/development

Pm

Mean arterial pressure (kPa) measured through a CAM artery

70 %

70 % of embryonic incubation/development for turtle embryos (~55 day total incubation)

90 %

90 % of embryonic incubation/development for turtle embryos (~55 day total incubation)

Supplementary material

360_2014_848_MOESM1_ESM.pdf (1.1 mb)
Supplementary Figs. S1–S7S1 shows a neighbor-joining phylogenetic tree comparing amino acid sequences of C. serpentina to two turtles, alligator, chicken, green anole, Tasmanian devil, mouse and human. The scale bar on S1 indicates the number of amino acid changes per site (the number of changes divided by sequence length), and the blackened sequences represent the seven transmembrane domains. S2 and S3 show amino acid and nucleotide alignments for Adora1 receptor, respectively, S4 and S5 show amino acid and nucleotide alignments for Adora2A receptor, respectively, and S6 and S7 show amino acid and nucleotide alignments for Adora2B receptor, respectively (PDF 1,174 kb)

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Department of BiologyMcMaster UniversityHamiltonCanada
  2. 2.Department of BiologyUniversity of North DakotaGrand ForksUSA
  3. 3.Department of Biological SciencesUniversity of North TexasDentonUSA

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