Objective To investigate changes in the delayed rectifier K+ channel (Kv) function and the regulation of Kv by the protein kinase C (PKC) pathway in bronchial myocytes from asthmatic rats.Methods The Kv currents and membrane potentials in bronchial myocytes from asthmatic rats and from controls were observed, using whole cell voltage- and current-patch clamp techniques.Results Bronchial myocytes from asthmatic rats showed a significant reduction in Kv-current density (51.6±9.4 pA/pF, n=14, P<0.01) in comparison with those from control rats (72.4±12.3 pA/pF, n=14) at +50 mV. The current-voltage relationship curve exhibited a significant downward shift. Bronchial myocytes from asthmatic rats had no significantly different capacitances (P>0.05), but had more positive membrane potential ( P<0.01) compared with those from controls. 1 μmol/L phorbol 12-myristate 13-acetate, a PKC activator, caused an obvious reduction in Kv-current density (P<0.01) and a significant downward shift in the current-voltage relationship curve, an effect which was partly abolished by 1 μmol/L Ro31-8220 (a PKC inhibitor); 1 μmol/L phorbol 12-myristate 13-acetate caused more positive membrane potential (Em), from -36.8±5.7 mV to -30.4±7.3 mV, in rat bronchial myocytes (P<0.05). This effect was partly abolished by 1 μmol/L Ro31-8220.Conclusions Bronchial myocytes from asthmatic rats have inhibited Kv function, more positive membrane potential, and higher excitability, all of which can also be induced by PKC activation. These characteristics may contribute to the development of airway hyperreactivity in asthma.