Delayed rectifier K + current of dog bronchial myocytes: effect of pollen sensitization and PKC activation

The properties of delayed rectifier K current [ I ] of canine airway smooth muscle cells isolated from small bronchi and its modulation by protein kinase C (PKC) were studied by whole cell patch clamp. I activated positive to -40 mV, with half-maximal activation at -16 ± 1.2 mV ( n = 15) and average current density of 31 ± 2.6 pA/pF ( n = 15) at +30 mV. The capacitive surface area, current density, and voltage dependence of activation of I of myocytes of ragweed pollen-sensitized dogs were not different from age-matched control dogs. However, the sensitization reduced the availability of I between -40 and -20 mV due to a hyperpolarizing shift in the voltage dependence of steady-state inactivation (-29.9 ± 1.2 in sensitized versus -26.0 ± 0.7 mV in control dogs, n = 9 and 11, respectively; P < 0.05). PKC activation with diacylglycerol analog or phorbol ester depressed I amplitude, whereas an inactive diacylglycerol analog had no effect. The hyperpolarizing shift in voltage dependence of inactivation and/or modulation of I by PKC may be two mechanisms that contribute to the enhanced reactivity of bronchial tissues from ragweed pollen-sensitized dogs.