Role of Ca 2+ in phosphatidylinositol 4,5‐bisphosphate (PIP 2 )/IP 3 ‐induced stimulation of the electrogenic Na/bicarbonate cotransporter NBCe1‐C heterologously expressed in Xenopus laevis oocytes

We previously showed that injecting ~10 μM (final) PIP 2 into a whole oocyte expressing NBCe1‐C stimulates an NBC‐mediated, HCO 3 − ‐induced outward current (I NBC ) by ~150%— an effect that is mimicked by injecting ~10 μM IP 3 (~180% stimulation), and blocked by depleting ER Ca 2+ stores by preincubating oocytes in 0‐Ca 2+ media containing thapsigargin (TG) + EGTA. Using the 2‐electrode voltage‐clamp technique, we have further examined the role of intracellular Ca 2+ (Ca 2+ i ) in PIP 2 /IP 3 ‐induced stimulation of I NBC in oocytes (V h = −60 mV) expressing rat NBCe1‐C. Consistent with IP 3 stimulation of NBCe1‐C, preincubating oocytes in the phospholipase C inhibitor U‐73122 decreased PIP 2 stimulation of I NBC to 48% ± 9% (n=6), whereas activating the endogenous G q ‐coupled GPCR with 1 μM lysophosphatidic acid stimulated I NBC 166% ± 43% (n=5). For oocytes bathed in 0‐Ca 2+ solutions to eliminate extracellular Ca 2+ (Ca 2+ o ) influx, injecting 100 nM IP 3 stimulated I NBC (142% ± 10%; n=5) to a similar degree as injecting 1 μM IP 3 (159% ± 7%; n=4) or 10 μM IP 3 (149% ± 15%; n=6). Ca 2+ o influx also stimulated I NBC . Returning bath Ca 2+ following TG+EGTA‐induced ER Ca 2+ ‐store depletion (which activates store‐operated Ca 2+ channels) stimulated I NBC by 224% ± 40% (n=6), as did applying 1 μM ionomycin (~100% stimulation; n=2). Similar results were obtained with NBCe1‐B, but not NBCe1‐A. In summary, PIP 2 injection can stimulate NBCe1‐B/C expressed in oocytes by increasing IP 3 and elevating Ca 2+ i . NIH NS046653, AHA 0755255B