Ketamine inhibits agonist-induced cAMP accumulation increase in human airway smooth muscle cells

Cyclic 3',5' adenosine monophosphate (cAMP) is a second messenger of the beta adrenergic receptor (betaAR). Ketamine causes an increase in the intracellular accumulation of cAMP in several non-human tissue preparations. A "species effect" may explain the differing results of ketamine on betaAR mediated responses, thus reports of a ketamine-induced increase in cAMP in other species may not be applicable to humans. The effect of ketamine (10(-3), 10(-4), or 10(-5) M) pretreatment (60 and 120 min) on isoproterenol [ISO, a beta adrenergic receptor (AR) agonist] or forskolin [FSK, an activator of adenylylcyclase (AC)]-induced intracellular accumulation of cAMP in a human airway smooth muscle (tracheal) cell line (HASM) was evaluated. In an in vitro HASM culture, cells with or without pretreatment were labeled with [3H]adenine to produce [3H]ATP, and following stimulation with ISO or FSK to convert the [3H]ATP to [3H]cAMP, the intracellular accumulation of [3H]cAMP was measured by sequential chromatography over Dowex and alumina columns. Pretreatment of the HASM cells with ketamine (10(-3) and 10(-4) M) caused a reduction (P < 0.05, when compared to untreated cells) in ISO-induced cAMP accumulation, but did not effect cAMP accumulation following FSK stimulation. This effect of ketamine was greater at 120 min of pretreatment than at 60 min (10(-3) M ketamine only)(P < 0.05). No effect was found at either time period following pretreatment of the HASM cells with ketamine 10(-5) M. These results demonstrate that pretreatment of the HASM cells with ketamine reduces ISO-induced cAMP accumulation. Since only ISO-induced cAMP was effected by ketamine, these data suggest that ketamine inhibits production of cAMP proximal to AC in the cAMP production pathway. These results also demonstrate that a mechanism other than that involving the betaAR and intracellular cAMP accumulation is responsible for the ketamine induced bronchodilation in humans.