Phosphatidylinositol 4,5‐bisphosphate (PIP 2 ) stimulation of electrogenic Na/bicarbonate cotransporter NBCe1 variants expressed in Xenopus laevis oocytes

Signaling molecules such as PKA/cAMP, PKC, and ATP modulate the activity of NBCe1. We recently discovered that cytosolic PIP 2 stimulates heterologously expressed rat NBCe1‐A in inside‐out macropatches excised from oocytes. To characterize the effect of PIP 2 on the activity of the three rat NBCe1 variants (‐A, ‐B, and ‐C), we used the 2‐electrode, voltage‐clamp technique to monitor repetitive HCO 3 − ‐induced outward currents (I NBC ) at ‐60 mV before and after injecting NBCe1‐expressing oocytes with PIP 2 (10/20 μM, estimated final). Injecting PIP 2 into an oocyte expressing NBCe1‐C caused a progressive rise (over ~15 min) in I NBC and a peak stimulation of 146±13% (n=10) of the initial pre‐injection I NBC , followed by a partial decline. Similar results were obtained with oocytes expressing NBCe1‐B (same N terminus), but not NBCe1‐A (different N terminus), which exhibited a stimulation of only 9±1% (n=4) after 10 min. For the C variant, injecting H 2 O or low levels of PIP 2 (~1 μM) had little effect on I NBC , whereas injecting IP 3 (~10/20 μM) modestly stimulated I NBC by 39±15% (n=4) after ~15 min. The PIP 2 stimulation of I NBC was reduced in oocytes expressing an NBCe1‐C missing its N‐terminal 87 residues. In summary, PIP 2 differentially modulates whole‐cell currents elicited by NBCe1 variants expressed in oocytes, and the N terminus found in the B and C variants contributes to injected PIP 2 stimulation of NBCe1 activity. Altered regulation of NBCs by PIP 2 during energy‐deficient conditions may contribute to changes in intracellular pH, Na + , and Ca 2+ with hypoxia and ischemia. NIH NS046653 ; AHA 0755255B