Transepithelial pressure pulses induce nucleotide release in polarized MDCK cells

The release of nucleotides is involved in mechanosensation in various epithelial cells. Intriguingly, kidney epithelial cells are absolutely dependent on the primary cilium to sense changes in apical laminar flow. During fluid passage, the renal epithelial cells are subjected to various mechanical stimuli in addition to changes in the laminar flow rate. In the distal part of the collecting duct, the epithelial cells are exposed to pressure changes and possibly distension during papillary contractions. The aim of the present study was to determine whether nucleotide release contributes to mechanosensation in kidney epithelial cells, thereby establishing whether pressure changes are sufficient to produce nucleotide-mediated responses. Madin-Darby canine kidney (MDCK) cells grown on permeable supports were mounted in a closed double perfusion chamber on an inverted microscope. The intracellular Ca(2+) concentration ([Ca(2+)](i)) was monitored with the Ca(2+)-sensitive fluorescence probe fluo 4. Transepithelial pressure pulses of 30-80 mm Hg produced a transient increase in [Ca(2+)](i) of MDCK cells. This response is independent of the primary cilium, since it is readily observed in immature cells that do not yet express primary cilia. The amplitudes of the pressure-induced Ca(2+) transients varied with the applied chamber pressure in a quantity-dependent manner. The ATPase apyrase and the P2Y antagonist suramin significantly reduced the pressure-induced Ca(2+) transients. Applying apyrase or suramin to both sides of the preparation simultaneously nearly abolished the pressure-induced Ca(2+) response. In conclusion, these observations suggest that rapid pressure changes induce both apical and basolateral nucleotide release that contribute to mechanosensation in kidney epithelial cells.