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.