Hydrogen peroxide induced responses of cat tracheal smooth muscle cells

1. The effects of hydrogen peroxide (H₂O₂) (10^-6-10^-3 M) on membrane potential, membrane currents, intracellular calcium concentration, resting muscle tone and contractions elicited by electrical field stimulation (EFS) and carbachol were examined in cat tracheal strips and isolated smooth muscle cells. 2. H₂O₂ (10^-4 and 10^-5 M) enhanced the amplitude of contractions and excitatory junction potentials (e.j.p.) evoked by EFS without changing muscle tone and resting membrane potential of the tracheal smooth muscle, and enhanced the contraction induced by carbachol (10^-8 M). At an increased concentration (10^-3 M), H₂O₂ elevated resting muscle tone and marginally hyperpolarized the membrane in the majority of the cells. 3. In 51 out of 56 cells examined, H₂O₂ (10^-6-10^-3 M) elicited an outward current at a holding potential of -40 mV and enhanced the frequency of the spontaneous transient outward current (STOC). In 20 cells the outward current was preceded by a small inward current. In the other cells, H₂O₂ elicited only an inward current or did not affect the background current. 4. In Ca²⁺ free solution the action of H₂O₂ on the resting muscle tone, STOCs, background current and on the current induced by ramp depolarization was significantly reduced. 5. H₂O₂ (10^-4 M) increased the intracellular ionized calcium concentration both in the absence and presence of external Ca²⁺. However, the effect developed faster and was of a higher amplitude in the presence of external Ca²⁺. 6. These results suggest that H₂O₂ increases intracellular Ca²⁺, with a subsequent augmentation of stimulation-evoked contractions, and enhances Ca²⁺ and voltage-sensitive potassium conductance.