Effect of the removal of extracellular Ca2+ on the response of cytosolic concentrations of Ca2+ to ouabain in carotid body glomus cells of adult rabbits.

Effect of the removal of extracellular Ca2+ on the response of cytosolic concentrations of Ca2+ (Ca2+]i) to ouabain, an Na+/K+ exchanger antagonist, was examined in clusters of cultured carotid body glomus cells of adult rabbits using fura-2AM and microfluorometry. Application of ouabain (10 mM) induced a sustained increase in Ca2+]i (mean+/-S.E.M.; 38+/-5% increase, n=16) in 55% of tested cells (n=29). The ouabain-induced Ca2+]i increase was abolished by the removal of extracellular Na+. D600 (50 microM), an L-type voltage-gated Ca2+ channel antagonist, inhibited the Ca2+]i increase by 57+/-7% (n=4). Removal of extracellular Ca2+ eliminated the Ca2+]i increase, but subsequent washing out of ouabain in Ca2+-free solution produced a rise in Ca2+]i (62+/-8% increase, n=6, P<0.05), referred to as a Ca2+]i rise after Ca2+-free/ouabain. The magnitude of the Ca2+]i rise was larger than that of ouabain-induced Ca2+]i increase. D600 (5 microM) inhibited the Ca2+]i rise after Ca2+-free/ouabain by 83+/-10% (n=4). These results suggest that ouabain-induced Ca2+]i increase was due to Ca2+ entry involving L-type Ca2+ channels which could be activated by cytosolic Na+ accumulation. Ca2+ removal might modify the Ca2+]i response, resulting in the occurrence of a rise in Ca2+]i after Ca2+-free/ouabain which mostly involved L-type Ca2+ channels.