Relationship between intracellular calcium and airway reactivity in guineapigs

The present study was carried out to examine the relationship between intra cellular free calcium ion concentrations and its regulatory enzymes, sodium potassium adenosine triphosphatase (Na+,K+-ATPase) and calcium adenosine t riphosphatase (Ca2+-ATPase), with airway reactivity to inhaled histamine in guinea pigs. Forty-nine guinea pigs were included in this study. Of these, 34 animals responded to histamine bronchoprovocation challenge in vivo wit h a greater than 35% fall in specific airways conductance and were labeled as "reactive," and the remaining 15 were "nonreactive." The dose of histami ne producing a 35% fall in specific airways conductance was labeled as ED35 SGaw. The animals were then sacrificed, and the following biochemical meas urements were carried out: intracellular free calcium ion concentrations [C a2+](i) in leukocytes and isolated tracheal smooth muscle cells, activities of Na+,K+-ATPase and Ca2+- ATPase in tracheal homogenate, and plasma level s of lysophosphatidy/choline (LPC). Reactive guinea pigs showed significant ly higher [Ca2+](i) and Na+,K+-ATPase and Ca2+-ATPase activities. Airway re activity (ED35 SGaw) had significant negative correlation with [Ca2+](i), w ith activities of each of the ATPases and with plasma lysophosphatidylcholi ne. It is concluded that the level of [Ca2+](i) is an important determinant of airway reactivity. Intracellular calcium levels modulate airway respons e to histamine with higher levels being associated with greater reactivity.