Inhibition of mechanical strain-induced fetal rat lung cell proliferation by gadolinium, a stretch-activated channel blocker.

Normal growth of the fetal lung is dependent upon fetal breathing movements. We have previously demonstrated that mechanical strain, simulating fetal breathing movements, stimulated DNA synthesis and cell division by reaggregated alveolar-like structures of fetal rat lung cells. Herein, we report that both intracellular and extracellular calcium modulate strain-induced proliferative activity. Strain-induced cell proliferation was inhibited by BAPTA/AM, an intracellular calcium chelator. The intracellular calcium modulators, cyclopiazonic acid and 2,5-di-(tert-butyl)-1,4-benzohydroquinone, increased DNA synthesis of unstrained cultures and partially reduced strain-induced cell growth activity. A similar effect was noted with the calcium ionophore A23187. Extracellular Ca2+ increased DNA synthesis in unstrained cultures in a concentration-dependent fashion. The stimulatory effect of strain on DNA synthesis was also dependent on the calcium concentration in the medium. Furthermore, strain-enhanced DNA synthesis was inhibited by the presence of a divalent ion chelator, EGTA, in the medium. Mechanical strain increased 45Ca2+ influx within 1 min after the onset of strain. This rapid entry of calcium was not affected by calcium channel blockers, such as verapamil or Ni2+. Calcium channel blockers verapamil, nifedipine, Ni2+, Co2+, or La3+ also did not inhibit strain-induced cell growth activity. In contrast, gadolinium, a stretch-activated channel blocker, inhibited strain-induced 45Ca2+ influx and suppressed strain-enhanced DNA synthesis. We conclude that the entry of calcium into cells through stretch-activated ion channels plays a critical role in strain-induced fetal lung cell proliferation.