Calcium entry stimulated by swelling of Madin-Darby canine kidney cells

Cell swelling in Madin-Darby canine kidney (MDCK) cells by reduction of extracellular osmolarity (omission of 70 and 150 mmol/l mannitol, respectively) leads to the activation of anion channels and Ca(2+) sensitive K(+) channels. The K(+) channel activation leads to an initial transient hyperpolarization of the cell membrane potential (PD) followed by a sustained depolarization due to activation of anion channels. The present study elucidates the role of intracellular calcium (Ca(i)(2+)) in regulatory cell volume decrease (RVD) of MDCK cells. While reduction of extracellular osmolarity by omitting 70 mmol/l mannitol did not lead to a detectable change in Ca(i)(2+), severe cell swelling by omitting 150 mmol/l mannitol led to a transient rise in Ca(i)(2+). PD changes, on the other hand, were not different under either condition. In addition, the response of PD to cell swelling was not altered by treatment of the cells with 12-O-tetradecanoylphorbol-13-acetate diester, pertussis toxin or cholera toxin. In the nominal absence of extracellular Ca(2+), reduction of extracellular osmolarity did not lead to an increase in Ca(i)(2+) and no initial transient hyperpolarization was observed, whereas addition of 10 mu mol/l ATP still led to a significant hyperpolarization. Omission of extracellular Ca(2+) was followed by a strong decrease in cell membrane resistance (R(m)) due to activation of a depolarizing cation conductance. Subsequent readdition of Ca(2+) caused a marked increase in Ca(i)(2+) due to Ca(2+) influx. This Ca(2+) entry was further stimulated by cell swelling. RVD was significantly blunted in the absence of extracellular Ca(2+). The results suggest that cell swelling stimulates a Ca(2+)-permeable pathway in the cell membrane favoring Ca(2+) entry into the cell with subsequent activation of Ca(2+)-sensitive K(+) channels.