Electrical properties of sodium bicarbonate symport in kidney epithelial cells (BSC-1)

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Abstract
Intracellular potentials of BSC-1 kidney epithelial cells known to express a .**GRAPHIC**. symport ranged between -40 and -70 mV, mean value Vm = -55.1 .+-. 10.1 mV. Lowering .**GRAPHIC**. at constant partial pressure of CO2 (PCO2) or complete removal of .**GRAPHIC**. rapidly depolarized, whereas readding .**GRAPHIC**. hyperpolarized Vm (40 .+-. 8 mV/decade .**GRAPHIC**. at constant PCO2). This response was largely reduced by 1 mM 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid (DIDS) (which depolarized Vm to about -20 mV) and in Na+-free medium, but Ba2+ had no effect. In .**GRAPHIC**. -Ringer, Na+ removal rapidly depolarized Vm (by 32 .+-. 7 mV), and readdition hyperpolarized Vm. This was reduced in .**GRAPHIC**. -free medium or by 1 mM DIDS but not by amiloride (10-5 and 10-3 M) or ouabain (10-4 M). In the absence of .**GRAPHIC**. and/or Na+, steady-state Vm was reduced to -12 .+-. 5 mV. Cl- removal had no effect on the responses to Na+ and/or .**GRAPHIC**. and led to a slow steady-state depolarization. Both in the presence and absence of .**GRAPHIC**. raising pHi (changed by NH4Cl or butyrate) depolarized, whereas lowering pHi hyperpolarized Vm. Lowering pHo in .**GRAPHIC**. -free Ringer depolarized Vm (23 .+-. 4 mV/decade H+). The slope conductance for K+ is only 6 .+-. 2 mV/decade. Thus BSC-1 cells display typical electrical characteristics of .**GRAPHIC**. symport. In contrast to other systems, the data are compatible with a net electrogenic inward transport of Na+ and .**GRAPHIC**. There might be an additional H+-(OH-) conductance operating also under nominally bicarbonate-free conditions.