Abstract
The present study was carried out to examine the relationship between intracellular free calcium ion concentrations and its regulatory enzymes, sodium potassium adenosine triphosphatase (Na+,K+-ATPase) and calcium adenosine triphosphatase (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 with a greater than 35% fall in specific airways conductance and were labeled as "reactive," and the remaining 15 were "nonreactive." The dose of histamine producing a 35% fall in specific airways conductance was labeled as ED35 SGaw. The animals were then sacrificed, and the following biochemical measurements were carried out: intracellular free calcium ion concentrations [Ca2+]i in leukocytes and isolated tracheal smooth muscle cells, activities of Na+,K+-ATPase and Ca2+-ATPase in tracheal homogenate, and plasma levels of lysophosphatidylcholine (LPC). Reactive guinea pigs showed significantly higher [Ca2+]i and Na+,K+-ATPase and Ca2+-ATPase activities. Airway reactivity (ED35 SGaw) had significant negative correlation with [Ca2+]i, with activities of each of the ATPases and with plasma lysophosphatidylcholine. It is concluded that the level of [Ca2+]i is an important determinant of airway reactivity. Intracellular calcium levels modulate airway response to histamine with higher levels being associated with greater reactivity.
