Abstract
The effect of maturation on the Na+-K+ pump of airway smooth muscle (ASM) was studied. Na+-K+ pump activity of tracheal smooth muscle from immature (1- to 2-week-old) and mature. (10-to 12-week-old) guinea pigs was measured as the ouabain-sensitive component of the resting membrane potential and as ouabain-sensitive 86Rb+ uptake (using 86Rb+ as a marker for K+). Maturation resulted in decreases in both the contribution of the Na+-K+ pump to the resting membrane potential and in ouabain-sensitive 86Rb+ uptake. 86Rb+ efflux from tracheal smooth muscle was similar in tissues from immature and mature guinea pigs, suggesting that maturation has no effect on K+ (or at least 86Rb+) permeability. Na+ and K+ contents of tracheal smooth muscle were estimated from the uptakes of 24Na+ and 86Rb+ at equilibrium. Maturation resulted in a decrease in Na+ content but had no effect on K+ content. Since intracellular Na+ is one of the principal determinants of Na+-K+ pump activity, these results suggest that maturation results in a decrease in Na+-K+ pump activity in ASM, which may be due to a decrease in Na+ content.
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