Phosphatidylinositol 4,5‐bisphosphate (PIP2) stimulates the electrogenic Na/bicarbonate cotransporter NBCe1‐A

Electrogenic NBCs that regulate intracellular pH and contribute to HCO 3 − transport are regulated by second messenger systems. We used the macropatch technique to study regulation of heterologously expressed rat NBCe1‐A in inside‐out patches from Xenopus oocytes. Exposing the cytosolic side of patches to a 33‐mM HCO 3 − solution elicited a mean inward NBC current (I NBC ) of 13±1 pA (n=114) in 83% of patches attached to pipettes (−Vp = −60 mV) containing a low‐Na + , nominally HCO 3 − ‐free solution. I NBC was 74±2% smaller in the absence of Na + (n=15), 79±10% smaller in the presence of 200 μM DIDS (n=6), and absent in patches from H 2 O‐injected oocytes (n=15). I NBC usually exhibited a Mg 2+ ‐sensitive, time‐dependent rundown, possibly due in part to phosphatase‐induced hydrolysis of PIP 2 . Indeed, the PIP 2 charge screeners neomycin, spermine, and poly‐lysine all reduced I NBC . Applying 10 μM PIP 2 (diC8) in the presence of HCO 3 − increased I NBC in 77% of patches from NBC‐injected, but not H 2 O‐injected oocytes. PIP 2 ‐ induced NBC stimulation was smaller in patches exhibiting larger initial HCO 3 − ‐induced I NBC . In experiments in which I NBC ranged from 0.5 to 20 pA, PIP 2 stimulated I NBC by 183±12% (n=22). Neomycin inhibited the PIP 2 ‐stimulated I NBC by 71±7% (n=4). In summary, exogenous and endogenous PIP 2 can stimulate NBCe1 activity, and phospholipids are newly discovered regulators of HCO 3 − transporters. NIH NS046653