2011 年 53 巻 4 号 p. 304-311
Imaging analysis using multiphoton microscopy revealed that rat parotid ductal cells exhibit spontaneous Ca2+ oscillations in the absence of calcium mobilizing agonist stimulation. This spontaneous Ca2+ release was first observed during the monitoring of Ca2+ transients during continuous perfusion at 37°C, and the protocol for cell preparation was modified to allow consistent observation of spontaneous oscillations. Spontaneous Ca2+ oscillations were completely blocked by application of the purinergic receptor inhibitors PPADS and suramin. Simultaneous observation of fura-2 fluorescence and differential interference contrast (DIC) images showed that spontaneous elevations in intracellular Ca2+ concentration ( [Ca2+] i) were well correlated with changes in the shape of ductal cells. Using a plasma membrane fluorescence probe we found that the changes in DIC images reflected spontaneous cell swelling of ductal cells. The present findings suggest the possibility that purinergic receptors mediate spontaneous Ca2+ oscillations in parotid ductal cells and regulate electrolyte reabsorption from the primary saliva under resting conditions. Cell swelling concomitant with a spontaneous increase in [Ca2+] i was an unexpected result because an agonist-induced increase in [Ca2+] i has been shown to induce cell shrinkage in ductal cells. When spontaneous Ca2+ release was compared to the carbachol-induced Ca2+ response, there were significant differences in the speed of Ca2+ elevation and duration of the Ca2+ response. Our data suggest that the different patterns of Ca2+ responses in parotid ducts might activate different ion channels and/or ion transporters and cause opposite cell shape changes.