Effects of purinoceptor agonists on cytosolic Ca2+ concentration in swine tracheal smooth muscle cells in culture.

1. The effects of various purinoceptor agonists on intracellular Ca2+ concentration ([Ca2+]i) in swine tracheal smooth muscle cells in primary culture were examined to investigate the subtype of purinoceptors in these cells. 2. ATP (1 microM to 1 mM) concentration-dependently increased [Ca2+]i which was measured by monitoring the fluorescence signal of fura2. 3. alpha, beta-Me ATP at concentrations higher than 10 microM increased [ca2+]i in the presence of extracellular Ca2+. Responses to the drug were 12 +/- 5 and 61 +/- 4% of responses to ATP (100 microM) at 100 microM and 1 mM, respectively (n = 7). The response to 100 microM ATP was inhibited by 62% in the presence of 1 mM alpha, beta-Me ATP (n = 8), though the drug at concentrations lower than that did not affect the response to ATP. 4. ATP increased [Ca2+]i in the absence of extracellular Ca2+. The response to ATP in this condition was 40% of that in the presence of extracellular Ca2+ (n = 8). 5. Neither cibacron blue 3GA (10 microM) (n = 8) nor suramin (10 and 100 microM) (n = 10) affected the response to ATP (1 microM to 100 microM). 6. The rank order of potency in the absence of extracellular Ca2+ was UTP > ATP > adenosine 5'-o-(3-thiotriphosphate) > > ADP = alpha, beta-methylene adenosine 5'-triphosphate > 2-(methylthio)-adenosine 5'-(tetrahydrogen triphosphate). 7. UTP (1 microM to 100 microM) concentration-dependently increased inositol 1,4,5-triphosphate (IP3) production. 8. These results suggest that the increase in [Ca2+]i induced by purinoceptor agonists is mediated mainly via a nucleotide receptor in swine tracheal smooth muscle cells in primary culture.