Effects of hypoxia and toxicant exposure on phosphoarginine, intracellular pH, and free Mg2+ in abalone as measured by 31P-NMR

The effects of hypoxia, sodium azide and pentachlorophenol (PCP) exposure on high-energy phosphorylated compounds, intracellular pH (pH_i) and intracellular free Mg²⁺ (Mg_f) in intact red abalone (Haliotis rufescens) were determined using ³¹P-NMR. Abalone made hypoxic by bubbling sea water with N₂ showed modest changes in phosphoarginine (PA) and inorganic phosphate (P_i) concentrations, no significant changes in pH_i and a moderate decrease in Mg_f that was not statistically significant. Azide (50 mg/l) exposed animals displayed severe declines in PA dropping to 0.53 of reference values, coupled with large increases in P_i to 10.66 times resting concentrations that occurred just after the 2-hr exposure period. pH_i also showed significant declines from a resting value of 7.17-7.06 (P < 0.05) but fully recovered by the end of the 6-hr clean seawater recovery period, whereas Mg_f concentrations declined slightly during the exposure period but increased by 18% at the end of the recovery period relative to reference Mg_f. PCP (1.2 mg/l) exposed animals displayed similar increases and declines in P_i and PA, respectively, as did azide-exposed animals by the end of the exposure period, but recovery was much slower and occurred in a bimodal fashion with some animals completely recovering at the end of 6 hr and others essentially stabilized at the end of the exposure period and did not show any significant changes during the recovery period.