The mechanism mediating regenerative intercellular Ca2+ waves in the blowfly salivary gland

Intercellular Ca2+ signaling in intact salivary glands of the blowfly Calli phora erythrocephala was studied by fluorimetric digital imaging combined w ith microinjection of putative messenger molecules. Iontophoretic injection of D-myo-inositol 1,4,5-trisphosphate (InsP(3)) into salivary gland cells evoked regenerative intercellular Ca2+ waves that spread through the impale d cell and several rows of surrounding cells. Ca2+ increases induced by mic roinjection of Ca2+ ions were confined to the injected cells and their near est neighbors. Depletion of intracellular Ca2+ stores by thapsigargin pretr eatment did not alter the time course of the Ca2+ increase caused by Ca2+ i njection. However, activation of Ca2+ release became clearly evident when C a2+ was injected in the presence of serotonin (5-MT). Under these condition s, injection of Ca2+ triggered intercellular Ca2+ waves that consecutively passed through >10 cells. The phospholipase C inhibitor U73122 blocked 5-HT -induced Ca2+ increases but did not affect InsP(3)-dependent Ca2+ spiking a nd intercellular Ca2+ wave propagation. The results demonstrate that propag ation of agonist-evoked Ca2+ waves in the blowfly salivary gland requires s upra-basal [InsP(3)] but does not depend on feedback activation of phosphol ipase C. We conclude that the intra- and intercellular transmission of thes e Ca2+ waves is mediated by diffusion of Ca2+ and Ca2+ induced Ca2+ release via the InsP(3) receptor channel.