Intracellular acidosis blocks the basolateral Na-K pump in rabbit urinary bladder

The purpose of the experiments described in this paper was to examine the effect of intracellular pH on the basolateral Na+-K+-ATPase of rabbit urinary bladder cells. To modify the intracellular pH, we permeabilized the apical membrane of the bladder cells with the polyene antibiotic nystatin. To verify that the intracellular pH could be altered after nystatin treatment, the intracellular pH was monitored with pH-sensitive microelectrodes. (The normal intracellular pH was 7.1 +/- 0.11, n = 21.) After nystatin treatment, the intracellular pH over the range of pH 5.8 to 8.0 was indistinguishable from the mucosal pH. The cell-to-serosa, ouabain-inhibitable sodium flux showed a strong dependence on intracellular pH, with pH values more acidic or more alkaline than 7.4 producing substantial block. The magnitude of the alkaline block obeyed a sigmoidal relationship with a half block of Na+ flux near pH 8.1. The magnitude of the acidic block also obeyed a sigmoidal relationship with half block at pH 6.85. The combination of the two relationships produced a bell-shaped curve with a maximum between pH 7.3 and 7.6. The steepness of both relationships suggested that H+ ion was interacting with more than one site. At the normal intracellular pH (7.1), the Na pump was already partially blocked. This partial block, coupled with the steepness of the relationship between Na pump activity and intracellular H+ near pH 7.1, suggests that intracellular pH could be an important controlling factor for Na pump activity.(ABSTRACT TRUNCATED AT 250 WORDS)