Abstract
Savannah monitor lizards, Varanus exanthematicus, are unusual among air‐breathing, ectothermic vertebrates by maintaining arterial pH nearly constant during changes in body temperature (‐0.003 U °C‐1) in contrast to the typical α‐stat regulating strategy (‐0.015 to ‐0.017 U °C‐1) of most other ectotherms. Given the importance of pH in the control of ventilation, we examined the CO2/H+ sensitivity of neurons from the locus coeruleus (LC) region of Savannah monitor lizard brainstems. Whole‐cell patch clamp electrophysiology was used to record membrane voltage (Vm) in neurons within the LC region in brainstem slices; changes in firing rate of LC neurons were calculated from action potential recordings. Upon exposure to hypercapnic acidosis (HA) at 20°C, 60% of neurons significantly decreased firing rate (1.8±0.3 vs. 0.6±0.1 Hz; P<0.05). The percentage of LC neurons inhibited by HA is high at 20°C compared with published percentages from bullfrogs and rats. Increasing temperature to 30°C abolished the inhibited response to HA (2.4±0.9 Hz vs. 2.6±1.0 Hz; P=1.0). The large proportion of neurons inhibited by HA at 20°C may provide a mechanism whereby retention of whole body CO2 stores with cooling enables the pH‐stat regulation strategy of Varanus exanthematicus.Grant Funding Source: Supported by NSF IOS 1257338
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