Background Potassium (K +) channels are important in regulating cell membrane potential and excitability. Although bronchial myocytes from asthmatic rats show a significant reduction in voltage-dependent delayed rectifier potassium channel (Kv) current density and higher excitability, the activity and expression of Kv in human bronchial smooth muscle cells (HBSMCs) have never been studied. The ob jective of this study was to investigate the effect of passive sensitization by asthmatic serum on the activity of Kv and the expression of Kv isoform Kv1.5 in HBSMCs.Methods HBSMCs were randomly divided into two groups: control group (containing 10% serum from nonatopic individuals) and sensitized group (containing 10% asthmatic serum), then cultured for 24 hours. Whole-cell patch clamp, immunofluorescence staining, reverse transcription-polymerase chain reaction and Western blot techniques were used to study the effect of passive sensitization on the activity of Kv and the expression of Kv1.5 in HBSMCs.Results The membrane potential in passively sensitized HBSMCs was significantly depolarized to -(26.7±5.2) mV compared with -(41.3±6.4) mV in the cont rol group (P<0.01). Passive sensitization caused a significant inhibition of Kv currents in HBSMCs, resulting in a downward shift in the current-voltage (Ⅰ-Ⅴ) relationship curve. At +50mV, the peak Kv current density of passively sensitized HBSMCs was significantly decreased from (54.6±8.7) picoamperes per picofarad ( pA/pF) to (32.1±7.1) pA/pF (P<0.01). The expression level of Kv1.5 mRNA in passively sensitized HBSMCs was significantly lower than that in the control group (0.76±0.07 vs 1.04±0.13, P<0.05). The expression of Kv1.5 protein of passively sensitized HBSMCs was also significantly reduced compared to that from the control group (984±168 vs 2200±380, P<0.05).Conclusions The activity and expression of Kv were all decreased in HBSMCs passively sensitized by asthmatic serum compared with nonsensitized cells. These changes might be involved in the mechanisms of formation and development of asthma. Background Potassium (K +) channels are important in regulating cell membrane potential and excitability. Although bronchial myocytes from asthmatic rats show a significant reduction in voltage-dependent delayed rectifier potassium channel (Kv) current density and higher excitability, the activity and expression of Kv in human bronchial smooth muscle cells (HBSMCs) have never been studied. The ob jective of this study was to investigate the effect of passive sensitization by asthmatic serum on the activity of Kv and the expression of Kv isoform Kv1.5 in HBSMCs. Methods HBSMCs were randomly divided into two groups: control group (containing 10% serum from nonatopic individuals) and sensitized group (containing 10% asthmatic serum), then cultured for 24 hours. Whole-cell patch clamp, immunofluorescence staining, reverse transcription- polymerase chain reaction and Western blot techniques were used to study the effect of passive sensitization on the activity of Kv and the expression of K v1.5 in HBSMCs. Results The membrane potential in passively sensitized HBSMCs was significantly depolarized to - (26.7 ± 5.2) mV compared with - (41.3 ± 6.4) mV in the cont rol group (P <0.01). Passive sensitization caused a significant inhibition of Kv currents in HBSMCs, resulting in a downward shift in the current-voltage (I-V) relationship curve. At + 50mV, the peak Kv current density of passively sensitized HBSMCs was significantly decreased from (54.6 ± 8.7) picoamperes per picofarad (pA / pF) to (32.1 ± 7.1) pA / pF (P <0.01). The expression level of Kv1.5 mRNA in passively sensitized HBSMCs was significantly lower than that in the control group (0.76 ± 0.07 vs 1.04 ± 0.13, P <0.05). The expression of Kv1.5 protein of passively sensitized HBSMCs was also significantly reduced compared to that from the control group (984 ± 168 vs 2200 ± 380, P <0.05) .Conclusions The activity and expression of Kv were all decreased in HBSMCs passively sensitized by asthmatic serum compared with nonsensiti zed cells. Tthese changes might be involved in the mechanisms of formation and development of asthma.