Figure 5. Comparative estimates of the blunting effects of chronic opioids on CO₂-mediated responses in neonatal AMCs.

Comparison of the CO₂-induced changes in holding current at −60 mV in control (Aa) versus opioid-treated (Ab) cells; note the significant (*P < 0.05) inward shift in holding current normally seen in control cells during high CO₂ is abolished in opioid-treated cells. The variability in CO₂-induced changes in membrane potential is shown for control cells (Ba, Bb) versus opioid-treated cells (Ca, Cb); data of response frequency for each condition are summarized in D. Note that CO₂-induced action potential firing or spikes (Ba) or subthreshold depolarizations (Bb) occur frequently in untreated (control) cells (D), but is rare in opioid-treated cells (Cb, D). Also, the majority of opioid-treated cells fail to show either CO₂-induced membrane depolarization or spikes, i.e. are non-responsive (Ca, D), in contrast to untreated cells (D).