In vitro activity: Doxapram is a respiratory stimulant that inhibits TASK-1, TASK-3, TASK-1/TASK-3 heterodimeric channel function with EC50 of 410 nM, 37 μM, 9 μM, respectively. Doxapram preferentially stimulated the release of dopamine. It was also seen to directly inhibit Ca(2+)-independent K+ currents. Doxapram was a more potent inhibitor of the Ca(2+)-activated K+ currents recorded under control conditions. Doxapram (at 15-150 μM) also evoked 3H overflow in a concentration dependent manner, and doxapram-evoked release was inhibited by the Ca2+ channel blocker nifedipine (5 μM). The effects of doxapram on type I cells show similarities to those of the physiological stimuli of the carotid body, suggesting that doxapram may share a similar mechanism of action in stimulating the intact organ.

Kinase Assay: Doxapram inhibited TASK-1 (half-maximal effective concentration [EC50], 410 nM), TASK-3 (EC50, 37 microM), and TASK-1/TASK-3 heterodimeric channel function (EC50, 9 microM).

Cell Assay: Doxapram (1-100 microM) caused rapid, reversible and dose-dependent inhibitions of K+ currents recorded in type I cells (IC50 approximately 13 microM). doxapram was also seen to directly inhibit Ca(2+)-independent K+ currents. Doxapram was a more potent inhibitor of the Ca(2+)-activated K+ currents recorded under control conditions. Doxapram (10 microM) was without effect on L-type Ca2+ channel currents recorded under conditions where K+ channel activity was minimized and was also without significant effect on K+ currents recorded in the neuronal cell line NG-108 15, suggesting a selective effect on carotid body type I cells. The effects of doxapram on type I cells show similarities to those of the physiological stimuli of the carotid body, suggesting that doxapram may share a similar mechanism of action in stimulating the intact organ.