Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates the electrogenic Na/HCO3 cotransporter NBCe1-A expressed in Xenopus oocytes

Bicarbonate transporters are regulated by signaling molecules/ ions such as protein kinases, ATP, and Ca2+. While phospholipids such as PIP2 can stimulate Na-H exchanger activity, little is known about phospholipid regulation of bicarbonate transporters. We used the patch-clamp technique to study the function and regulation of heterologously expressed rat NBCe1-A in excised macropatches from Xenopus laevis oocytes. Exposing the cytosolic side of inside-out macropatches to a 5% CO2/33 mM HCO3- solution elicited a mean inward current of 14 pA in 74% of macropatches attached to pipettes (-Vp = -60 mV) containing a low-Na+, nominally HCO3--free solution. The current was 80-90% smaller in the absence of Na+, approximately 75% smaller in the presence of 200 mu M DIDS, and absent in macropatches from H2O-injected oocytes. NBCe1-A currents exhibited time-dependent rundown that was inhibited by removing Mg2+ in the presence or absence of vanadate and F- to reduce general phosphatase activity. Applying 5 or 10 mu M PIP2 (diC8) in the presence of HCO3- induced an inward current in 54% of macropatches from NBC-expressing, but not H2O-injected oocytes. PIP2-induced currents were HCO3--dependent and somewhat larger following more NBCe1-A rundown, 62% smaller in the absence of Na+, and 90% smaller in the presence of 200 mu M DIDS. The polycation neomycin (250-500 mu M) reduced the PIP2-induced inward current by 69%; spermine (100 mu M) reduced the current by 97%. Spermine, poly-D-lysine, and neomycin all reduced the baseline HCO3--induced inward currents by as much as 85%. In summary, PIP2 stimulates NBCe1-A activity, and phosphoinositides are regulators of bicarbonate transporters.