Assessment of evidence for K+-H+ exchange in isolated type-1 cells of neonatal rat carotid body.

Intracellular pH (pH_i) was measured in enzymically isolated, neonatal rat carotid body type-1 cells, using the fluorophore carboxy-SNARF-1 (AM-loaded), and using the nigericin technique for in situ fluorescence calibration (nigericin is a membrane-soluble K⁺-H⁺ exchanger). In CO₂/HCO₃ ^–-free media, inhibiting Na⁺-H⁺ exchange produced a prompt fall of pH_i (background acid-loading), the rate of which was reduced by raising the extracellular K⁺ concentration, [K⁺]_o. pH_i recovery from an intracellular acid or alkali load was also sensitive to changes of [K⁺]_o. These results are similar to those of Wilding et al. (J Gen Physiol 100:593–608, 1992), who proposed the existence of an acid-loading, K⁺-H⁺ exchanger (KHE) in the type-1 cell. However, when nigericin was not used for post-experimental calibration, and the superfusion system was flushed exhaustively with strong detergent, alcohol and distilled water, then background acid-loading was attenuated, and the K⁺ _o sensitivity of pH_i insignificant. Background loading was increased again, and K⁺ _o sensitivity restored, when cells were monitored in a superfusion system which had previously been exposed to a single nigericin-calibration protocol (followed by a short system wash with strong detergent and distilled water). We conclude that the previously reported expression of KHE in carotid body type-1 cells is an artefact caused by nigericin contamination. We have therefore quantified the pH_i dependence of background loading in uncontaminated type-1 cells. We consider the possible implications of our work for reports of KHE in other cell types. [ABSTRACT FROM AUTHOR]