Fig. 4.
Effect of cell-volume changes on NHE1 activity in CHO cells. Pipette perfusion with a hypertonic solution containing sucrose leads to cell swelling and reduction of NHE1 activity. (a) This is reversed by perfusion of hypotonic solution without sucrose, which restores cell volume. (b) Vice versa, perfusion of hypotonic solution leads to cell swelling and increase NHE1 activity, even under conditions of a normal pHi of 7.1. (c) At maximal activation of NHE1 activity (pHi 6 and pHo 8), volume sensitivity of NHE1 is lost. (d) In the absence of MgATP in the pipette solution and replacement by AMP-PNP, volume sensitivity of NHE1 is preserved. (e) Pipette perfusion with gelsolin to depolymerize F-actin does not affect NHE1 activity or NHE1 volume sensitivity.