Effects of potassium channel blockers on hyperinflation-induced rapidly adapting pulmonary stretch receptor...

The effects of K+ channel blockers, such as 4-aminoprydine (4-AP) and tetraethylammonium (TEA), on the excitatory responses of rapidly adapting pulmonary stretch receptor (RAR) activity to hyperinflation (inflation volume=3 tidal volumes) were investigated in anesthetized, artificially ventilated rabbits after vagus nerve section. The changes in the RAR adaptation index (AI) produced by constant-pressure (approximately 30 cmH2O, 29.7+/-0.2 cmH2O) inflation of the lungs were also examined before and after pretreatment with 4-AP and TEA. The administration of 4-AP (0.7 and 2.0 mg/kg) potentiated hyperinflation-induced RAR stimulation in a dose-dependent manner. During hyperinflation after 2.0 mg/kg 4-AP administration the discharge of RARs showed a relatively regular firing pattern in both inflation and deflation phases. The RAR AI values during constant-pressure inflation of the lungs were significantly reduced by 4-AP treatment (2.0 mg/kg). TEA treatment (2.0 and 7.0 mg/kg) did not significantly alter either the excitatory response of RAR activity to hyperinflation or the RAR AI values seen during constant-pressure inflation of the lungs. These results suggest that during hyperinflation in in vivo experiments on rabbits, RARs may be maintained at a lower activity by opening the 4-AP-sensitive K+ channels on the receptor endings, which can determine accommodation of the receptor discharge.