Erythrocytic nucleoside triphosphates in marine fish

Area of Science:

• Comparative Physiology
• Fish Biology
• Biochemistry

Background:

• Erythrocytic nucleotides play a crucial role in regulating hemoglobin-oxygen affinity in vertebrates.
• Understanding these nucleotide profiles in diverse fish species can reveal adaptive strategies.
• The Root effect, a reduction in blood oxygen-carrying capacity at low pH, is influenced by these nucleotides.

Purpose of the Study:

• To quantify whole blood purine nucleotides, specifically adenosine triphosphate (ATP) and guanosine triphosphate (GTP), in various selachian (sharks and rays) and marine teleost species.
• To investigate the relationship between erythrocytic nucleotide concentrations and hemoglobin-oxygen affinity.
• To explore how these nucleotide levels correlate with fish habits, habitats, and the expression of the Root effect.

Main Methods:

• Whole blood samples were collected from 19 species of selachians and 27 species of marine teleosts.
• Quantification of purine nucleotides (ATP and GTP) within erythrocytes was performed.
• Concentrations of total nucleotides (NTP) and the ratio of NTP to hemoglobin (Hb) were calculated.

Main Results:

• ATP and GTP were detected in the erythrocytes of nearly all studied fish species.
• ATP was identified as the primary modulator of oxygen affinity in rays, sharks, and teleosts.
• Erythrocytic NTP concentration and the NTP/Hb ratio were lowest in rays, intermediate in sharks, and highest in teleosts, indicating a gradient of nucleotide levels across these groups.

Conclusions:

• Intraerythrocytic phosphate content, particularly ATP and GTP, varies significantly among fish taxa.
• These variations likely represent distinct adaptive strategies related to ecological niches, behavior, and physiological oxygen-binding properties, including the Root effect.
• The findings highlight the conserved yet diverse roles of purine nucleotides in fish respiratory physiology.