Characteristics of 45Ca uptake and efflux in rat lung slices

The distribution and movements of 45Ca were investigated in lung slice preparations obtained from rats. The accumulation of 45Ca was measured in either 5.0 mM Ca2+, 0.5 mM Ca2+ or 0-Ca solutions. The 45Ca tissue to medium ratio was greatest in the 0-Ca solution; the presence of either 5.0 mM Ca2+ or 0.5 mM Ca2+ reduced this ratio 8- and 5-fold, respectively. Efflux of 45Ca indicated that there are at least two washout components. Exposure to either La3+ or Sr2+ (0.5 mM) during the washout resulted in a transient increase in 45Ca efflux (Sr2+ greater than La3+), whereas 0 degrees C slowed the loss of 45Ca. Uptake of 45Ca was increased by the metabolic inhibitor iodoacetic acid and inhibited in the presence of either La3+ or Sr2+. These findings indicate that the 45Ca accumulated within the lung is not readily depleted and a portion appears to accumulate at intracellular or less superficial sites or stores.