Evidence for electronogenic sodium pumping in the ductal epithelium of rabbit salivary gland and its relationship with (Na+ plus K+)-ATPase.

The temperature dependence of the transepithelial potential difference (PD) of the main duct of the submaxillary gland has been measured during in vitro perfusion studies. The magnitude of the PD depends strongly on the anion composition of the perfusing and bathing fluids. The following combinations of perfusion and bathing fluids respectively were used: (1) Na2SO4/NaCl, (2) Na2SO4, (3) NaCl/-NaCl, (4) NaCl/Na2SO4. The mean transepithelial potential differences at 35 degrees C with these four sets of conditions were respectively: 144, 148, 10 and - 15 mV, serosal side positive with respect to lumen. From the data obtained it was possible to construct Arrhenius plots of temperature dependence of the PD for the four sets of experimental conditions. They all show a breakpoint between 16 and 19 degrees C. The apparent activation energies in the four situations above the breakpoint are 4.2, 1.4, 12.0 and 10.6 kcal/mol, respectively. Below the breakpoint they are 29.9, 37.5, 29.0 and 31.3 kcal/mol, respectively. The rapid change in the PD as a function of temperature (which can also be achieved by the addition of ouabain), the effects of the removal of K+ on the serosal side on the PD, the decrease in the PD after the addition of ouabain or CN-, and the activation energies and breakpoints all lead to the conclusion that a large part of the PD is caused by an electrogenic sodium pump which is very probably the enzyme (Na+ plus K+)-ATPase. When the duct is perfused with Na2SO4 we find, above the breakpoint in the Arrhenius plots, a lower activation energy than is found when perfusing with NaCl.