The life cycle of the sea lamprey (Petromyzon marinus) is characterized by a terminal upstream spawning migration that may be associated with brief bursts of high-intensity swimming. Such activity usually leads to pronounced blood acid-base disturbances in fishes, but lampreys rapidly correct these perturbations within 1 h. In the present study, patterns of post-exercise H+ excretion (JHnet) and ion movements were followed in sea lampreys to test the hypothesis that dynamic manipulation of Na+ versus Cl- movements across the animal's body surface, presumably at the gills, accounted for the rapid restoration of blood pH following exercise. The first hour of post-exercise recovery in sea lampreys was associated with marked stimulation of JHnet (equivalent to base uptake), which approached -500 micromol kg-1 h-1. After 1 h, JHnet patterns had returned to resting rates. Analyses of net Na+ and Cl- movements (JNanet, JClnet) suggested that elevated net Cl- losses, which greatly exceeded net Na+ losses, accounted for most of the JHnet. Subsequent experiments, using radiotracers (22Na+, 36Cl-), indicated that differential increases in Cl- versus Na+ permeability accounted for the greater post-exercise Cl- losses and the corresponding stimulation of net proton excretion. Finally, metabolic acid budget analyses confirmed our hypothesis that rapid excretion of metabolic protons was the primary means used by sea lampreys to correct post-exercise extracellular acidosis. <P>

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