Effect of nitric oxide on potassium channels of rat airway smooth muscle cells.

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-cell 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 mode 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 protocol at 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 currents under ramp protocol from 389.6 +/- 84.1 pA to 526.7 +/- 98.7 pA (n = 7, P < 0.01), the currents under pulse protocol at 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 increases 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.