Temperature effects on CO 2-sensitive intrapulmonary chemoreceptors in the lizard, Tupinambis nigropunctatus

Abstract

Body temperature (Tb) effects on CO 2 responses of 17 intrapulmonary chemoreceptors (IPC) were investigated in 9 anesthetized (pentobarbital; 30 mg/kg) and unidirectionally ventilated tegu lizards ( Tupinambis nigropunctatus). At 30°C, all IPC (n = 15) had a stable discharge pattern. At 20°C, IPC discharge (n = 14) was stable at high P CO 2 but irregular at low P CO 2 and often ( 10 14 ) consisted of bursts of actively separated by one or more seconds of quiescence. Responses of IPC to static and dynamic changes in P CO 2 were quantified at both Tb and the discharge rate vs P CO 2 response curves were compared. Static discharge frequency (f stat) decreased as P CO 2 increased at both Tb. At 20°C: (1) f stat was diminished at all P CO 2 levels relative to 30°C; and (2) the slope of the f stat vs P CO 2 relationship was markedly attenuated. The Q 10 was 3.7 ± 0.5 and was independent of P CO 2 . The peak discharge associated with a step decrease in P CO 2 (dynamic response; f dyn) also decreased as P CO 2 increased. At 20°C: (1) f dyn was diminished at all P CO 2 levels relative to 30°C; but (2) the slope of the f dyn vs P CO 2 relationship was similar at both Tb. The Q 10 was 2.6 ± 0.3 and was significantly less than the Q 10 of f stat ( P < 0.05). Acute changes in Tb exert large effects on the CO 2 response and discharge pattern of IPC; these effects on IPC may be important in ventilatory control at different Tb in lizards.