Stimulation of KCl co-transport in equine erythrocytes by hydrostatic pressure: effects of kinase/phosphatase inhibition

The effects of hydrostatic pressure on the KCl co-transporter of equine erythrocytes were studied to determine factors involved in its regulation. Pressure (0.1–40MPa) increased Cl^–-dependent K⁺ transport; in the presence of the putative kinase inhibitor N-ethylmaleimide (NEM) which stimulates the transporter, or the phosphatase inhibitor calyculin A, pressure had no significant effect. The sequential application of NEM and calyculin A clamped the transporter at about 30% of maximal flux compared to NEM alone; pressure also had no further effect. These results suggest that pressure acts on the phosphorylation status of the transporter or regulatory peptide, rather than on the ion flux per se. Since the activation of the KCl co-transporter by pressure occurs without an apparent change in cell volume these results have implications for any universal model for the regulation of KCl co-transport.