Antibodies against the cardiac sodium/bicarbonate co-transporter (NBCe1) as pharmacological tools

Abstract

BACKGROUND AND PURPOSE Na +/HCO 3- co-transport (NBC) regulates intracellular pH (pH i) in the heart. We have studied the electrogenic NBC isoform NBCe1 by examining the effect of functional antibodies to this protein. EXPERIMENTAL APPROACH We generated two antibodies against putative extracellular loop domains 3 (a-L3) and 4 (a-L4) of NBCe1 which recognized NBCe1 on immunoblots and immunostaining experiments. pH i was monitored using epi-fluorescence measurements in cat ventricular myocytes. Transport activity of total NBC and of NBCe1 in isolation were evaluated after an ammonium ion-induced acidosis (expressed as H + flux, J H, in mmol·L -1 min -1 at pH i 6.8) and during membrane depolarization with high extracellular potassium (potassium pulse, expressed as ΔpH i) respectively. KEY RESULTS The potassium pulse produced a pH i increase of 0.18 ± 0.006 (n= 5), which was reduced by the a-L3 antibody (0.016 ± 0.019). The a-L-3 also decreased J H by 50%. Surprisingly, during the potassium pulse, a-L4 induced a higher pH i increase than control,(0.25 ± 0.018) whereas the recovery of pH i from acidosis was faster (J H was almost double the control value). In perforated-patch experiments, a-L3 prolonged and a-L4 shortened action potential duration, consistent with blockade and stimulation of NBCe1-carried anionic current respectively. CONCLUSIONS AND IMPLICATIONS Both antibodies recognized NBCe1, but they had opposing effects on the function of this transporter, as the a-L3 was inhibitory and the a-L4 was excitatory. These antibodies could be valuable in studies on the pathophysiology of NBCe1 in cardiac tissue, opening a path for their potential clinical use. © 2011 The Authors.