The role of calcium in cell shrinkage and intracellular alkalinization by bradykinin in Ha-ras oncogene expressing cells.
In ras oncogene expressing cells, bradykinin leads to intracellular alkalinization by activation of the Na+/H+ exchanger. This effect is paralleled by oscillatory increase of intracellular calcium activity and cell shrinkage. Staurosporine (1 mumol/l) is not sufficient to prevent bradykinin induced intracellular alkalinization, thus pointing to a protein kinase C independent pathway for the activation of Na+/H+ exchange. The present study has been performed to elucidate, whether the increase of intracellular calcium contributes to cell shrinkage and activation of the Na+/H+ exchanger. To this end, the effects of the calcium ionophore ionomycin have been tested. Ionomycin leads to a dose dependent increase of intracellular calcium activity. At 100 nmol/l ionomycin intracellular calcium is increased from 114 +/- 17 nmol/l to 342 +/- 24 nmol/l (n = 9), a value within the range of intracellular calcium concentrations following application of bradykinin. The calcium increase is paralleled by a decrease of cell volume by 12 +/- 2% (n = 5) and an increase of intracellular pH from 6.78 +/- 0.02 to 6.90 +/- 0.03 (n = 11), values similar to those following application of bradykinin. The alkalinizing effect of ionomycin is completely abolished in the presence of the novel Na+/H+ exchange inhibitor HOE 694 (10 mumol/l), but is not inhibited by 1 mumol/l staurosporine. Inhibition of K+ and Cl- channels by barium (5 mmol/l) and ochratoxin-A (5 mumol/l) prevents both ionomycin induced cell shrinkage and protein kinase C independent intracellular alkalinization. It is concluded that bradykinin leads to intracellular alkalinization mainly by increasing intracellular calcium concentration. Calcium triggers calcium sensitive K+ channels, and presumably Cl- channels, the subsequent loss of cellular KCl leads to cell shrinkage which, in turn, activates Na+/H+ exchange.
Wöll
E
E
Institute for Physiology, University of Innsbruck, Austria.
Ritter
M
M
Scholz
W
W
Häussinger
D
D
Lang
F
F
D016475:3T3 Cells; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D011905:Genes, ras; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D011189:Potassium Chloride / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D007473:Ion Channels; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D011189:Potassium Chloride; D001920:Bradykinin; D002118:Calcium