A transient calcium influx into airway smooth muscle cells induced by immunization

We have recently reported that sensitization induced biphasic changes of resting membrane potential of the airway smooth muscle cells (Souhrada and Souhrada, 1985). To further clarify whether these changes may have any effect on the airway smooth muscle contractility, we have studied tracheal segments, isolated from Camm-Hartley guinea pigs during passive in vitro sensitization. At that time, airway smooth muscle cells were frequently penetrated with glass microelectrodes and the value of the resting membrane potential was determined simultaneously with changes in the isometric force. It was found that: changes in the resting membrane potential were accompanied by the alteration of the isometric force; during the depolarization phase a transient increase in the isometric force was observed achieving the maximal peak equal to 800 +/- 50 mg; both electrical and contractile changes of airway smooth muscle preparations as induced by sensitization were dependent on the dilution of sensitized serum; ED50 of this relationship was equal to dilution of 1:2500, while the maximal depolarization and the maximal peak isometric force developed at the dilution of serum 1:10; sensitization-induced sodium influx was critical for the development of the isometric force and depolarization, since pretreatment of tissues with amiloride (10(-5) M) or tetrodotoxin (10(-7) M) attenuated these changes; an increase in the isometric force was related to both the opening of the voltage dependent calcium channels and the release of calcium from the intracellular pools.