Role of calcium in airway reactivity and asthma.

To the Editor : The recent article, "Sensitization alters contractile responses and calcium influx in human airway smooth muscle," (J ALLERGY CLIN IMMUNOL 1989 ;440-7) by Black et al .' has further contributed to the hypothesis that some alteration in the regulation of airway smooth muscle calcium may contribute another mechanism to bronchial hyperresponsiveness . The possible role of an abnormality in smooth muscle calcium homeostasis in the pathogenesis of airway reactivity was first reported by Weiss and Viswanath in 1979 . 2 We have extended our initial observation of an acquired alteration in calcium metabolism after in vitro anaphylaxis to implicate a role of toxic oxygen products in this process . Both enhanced myorelaxation in a (Ca"),-free medium and a leukotriene (LTD,)-induced synergism to histamine contractures (under physiologic 2 .5 mmol/L and 0 mmol/L extracellular calcium conditions) were significantly inhibited by superoxide dismutase in guinea pig trachealis .',' Both LTD, and superoxide anion (0,) have been demonstrated to be generated during experimental airway anaphylaxis .' Moreover, in children with asthma, leukocyte release of histamine was demonstrated to be significantly correlated with 0,generation . It is of interest that the studies of Black et al .' and other igators' reveal a somewhat different phenomenon, that is, an enhanced myocontractility to agonist histamine and an involvement of the calcium voltage-dependent channel to depolarizing KCI after passive sensitization without reactive immunogenic anaphylaxis . Given the experprotocol of Black et al .,' it would have been of some interest to retest the cited agonists in their system after specific Dermatophagoides farinae challenge . Collectively, the current observations suggest a possible direct role for a smooth muscle calcium alteration contributing to airway hyperresponsiveness, as occurs in asthma . A major element of smooth muscle tension development is an increase in intracellular calcium after a variety of chemical, electrical, or mechanical stimuli . However, a multiplicity of calcium mobilizing pathways can be involved in regulatory processes that influence smooth muscle tension and reactivity . Additional studies are clearly indicated to clarify the role of calcium in human airway reactivity ; studies by Black et al .' have further contributed to an exciting area of interest.