Effects of Na and K ions on the active Na transport in guinea-pig auricles

Abstract

1. The effect of Na and K ions on active Na transport was studied in guinea-pig auricles by means of flame photometry. 2. The Na influx into preparations rewarmed in Tyrode's solution after cooling was estimated to be about 1.05 mmole/l fibre water·min ((l.f.w.·min) or c. 8 pmole/cm²·s. Intracellular Na ions enhanced the active Na efflux over a wide range of concentrations. A decrease in the extracellular Na concentration ([Na] _o ) had no major effect on the active Na efflux. 3. Extracellular K ions initiated an active Na efflux from rewarmed auricles with an elevated [Na] _i over a narrow range of K concentrations ([K] _o ). 4. Assuming Michaelis-Menten kinetics the maximal active Na efflux activated by internal Na ions was calculated to be about 4 mmole/l.f.w.·min (30 pmole/cm²·s). Half maximal Na efflux occurred at about 22 mmole/l.f.w. [Na] _i . The maximal K-activated active Na efflux was deduced to be about 3.7 mmole/l.f.w.·min (28 pmole/cm²·s) and was half maximal at a [K] _o of about 0.2 mM. 5. It is tentatively concluded that the maximal active Na efflux from guinea-pig atria is 3–4 times larger than the physiological flux. Under normal conditions active Na efflux in heart is mainly regulated by variations of [Na] _i .