Oxygen Sensitivity in the Crayfish Procambarus clarkii: Peripheral O2 Receptors and Their Effect on Cardiorespiratory Functions

The intent of this study was to determine the location and functional influence of the branchial O2-sensitive receptors of the crayfish on cardiac and respiratory parameters. Crayfish (46.6 ± 1.7 g [±SD]) were divided into 3 groups (A) control (gills intact), (B) posterior gills removed, and (C) anterior gills removed. Animals were exposed to hypoxic water (1 h; 15 mm Hg O2 followed by left branchial injection (10 ml over 10 min) of hyperoxic water (400 mm Hg O2). The time course to changes in cardiorespiratory parameters (heart rate, cardiac output, stroke volume, arterial flows, ventilation rate, and branchial pressure) were monitored. Intact animals showed a rapid cardiovascular response to injection of hyperoxic water (2.5 s) with group C animals showing a similar response time. Group B animals exhibited a significantly longer response time (13.0 s). Ventilatory response time was similar for all 3 groups (75 s), the duration of the ventilatory response was 51.0 s in control and group C animals. Animals lacking posterior gills showed a significantly shorter response time (42.0 s). Time-course evidence may indicate the existence of 2 populations of O2 receptors, one responsible for modulation of cardiovascular functions on the posterior gills or in their cardiobranchial veins, the other responsible for ventilatory modulation located more centrally.