The effect of nitric oxide donor sodium nitroprusside (SNP) on resting membrane potential (Em) and potassium currents of the bronchial smooth muscle cells from rats was investigated. All experiments were conducted in conventional whole cel l configuration. The changes of Em and potassium currents after addition of 0.1 mmol/L SNP were measured under the current clamp mode and the voltage clamp mo de respectively. Results showed that (1) SNP could decrease the Em from -33.8±7 .4 mV to -43.7±6.7 mV ( n =10, P <0.01); (2) SNP could increase the Ca 2+ activated K + channel peak currents under ramp protocol from 466.9±180.1 pA to 597.7±237.6 pA ( n =7, P <0.01), and the currents under pulse proto col at +50 mV were increased from 544.2±145.4 pA to 678.1±206.2 pA ( n =6, P <0.05); (3) SNP also could increase voltage gated K + channel peak curren ts under ramp protocol from 389.6±84.1 pA to 526.7±98.7 pA ( n =7, P <0.0 1), the currents under pulse protocol at +50 mV were increased from 275.7±85.2 pA to 444.3±128.5 pA( n =6, P <0.01). It was concluded that SNP increa ses the activities of Ca 2+ activated K + channels and voltage gated K + channels and leads to K + efflux and hyperpolarization of the cell membrane, resulting in a decrease of the cell excitement.
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