Microtubules regulate local Ca2+ spiking in secretory epithelial cells

The role of the cytoskeleton in regulating Ca2+ release has been explored i n epithelial cells. Trains of local Ca2+ spikes were elicited in pancreatic acinar cells by infusion of inositol trisphosphate through a whole cell pa tch pipette, and the Ca2+-dependent Cl- current spikes were recorded. The s pikes were only transiently inhibited by cytochalasin B, an agent that acts on microfilaments, In contrast, nocodazole (5-100 mu M), an agent that dis rupts the microtubular network, dose-dependently reduced spike frequency an d decreased spike amplitude leading to total blockade of the response. Cons istent with an effect of microtubular disruption, colchicine also inhibited spiking but neither Me2SO nor beta-lumicolchicine, an inactive analogue of colchicine, had any effect. The microtubule-stabilizing agent, taxol, also inhibited spiking. The nocodazole effects were not due to complete loss of function of the Ca2+ signaling apparatus, because supramaximal carbachol c oncentrations were still able to mobilize a Ca2+ response. Finally, as visu alized by 2-photon excitation microscopy of ER-Tracker, nocodazole promoted a loss of the endoplasmic reticulum in the secretory pole region. We concl ude that microtubules specifically maintain localized Ca2+ spikes at least in part because of the local positioning of the endoplasmic reticulum.