Lack of effect of potassium on fluid absorption in isolated, perfused snake proximal renal tubules

Effects of alterations in potassium concentrations on net fluid absorption (Jv) by isolated, perfused snake (Thamnophis spp.) proximal renal tubules were studied. With standard (3 mmol/1 potassium, 150 mmol/1 sodium) Ringer’s solution in perfusate and bath, Jv was about 1.3 nl min^-1 mm^-1. Replacing potassium with sodium in perfusate or in both perfusate and bath had no significant effect on Jv. Increasing potassium concentration to 100 mmol/1 in place of sodium in perfusate or in both perfusate and bath also had no effect on Jv. Findings that potassium is not critical for maintaining Jv are also consistent with previous findings that sodium is not necessary for maintaining Jv.