We tested the effects of tetraethylammonium (TEA), acetylcholine (ACh), histamine, and endothelin-1 on single airway smooth-muscle cells from bovine trachea, using the patch-clamp technique. Resting membrane potential was -48 +/- 1 mV (n = 47). Both TEA and ACh significantly depolarized the membrane, by +28 +/- 4 mV (P < 0.001, n = 12) and +21 +/- 2 mV (P < 0.01, n = 7), respectively, in the whole-cell configuration. In contrast, both histamine and endothelin-1 hyperpolarized the membrane, by -21 +/- 6 mV (P < 0.01, n = 8) and -15 +/- 2 mV (P < 0.01, n = 8), respectively. Calcium-dependent large-conductance K+-channels (127 pS) and small-conductance K+ channels (21 pS) were identified in excised patches. The small-conductance K+ channel was inhibited by 4-aminopyridine and activated by both histamine and endothelin-1. Furthermore, TEA did not alter the membrane hyperpolarization by these agonists, suggesting that the small-conductance K+ channel or delayed-rectifier K+ channel was involved in the membrane hyperpolarization. Membrane hyperpolarization by histamine and endothelin-1 suggests that activation of voltage-dependent calcium channels (VDCCs) or of calcium influx does not contribute substantially to the contractile response of airway smooth-muscle contraction to these agonists.