Abstract
Abstract
A technique is presented to estimate the initial rates of Na+-dependent alkal-inization of acidified human fibroblasts and platelets and assess the kinetics of the Na+/ H+ antiport in these cells. Cytosolic pH (pH
i
) exhibits an exponential recovery following cellular acidification. Thus, the length of the time interval selected to monitor changes in pH
i
(ΔpH
i
) is critical to estimating the kinetics of the Na+/H+ antiport. We compared kinetic parameters of the Na+/H+ antiport, using computed and observed changes in ΔpH
i
, for arbitrarily selected time intervals following Na+-dependent activation. In both cells, significant increases in both the [Na+] for half-maximal activation (K
0.5) and maximal velocities (V
max) were observed as ΔpH
i
was decreased. We conclude that kinetic parameters derived from initial rate determinations enable a more accurate characterization of the Na+/H+ antiport.