Abstract
Using the spiral strips of pulmonary artery from rabbits, effects of the modified contents of Na and K in the bath solution (BS) (Locke solution) on the tonus and the contractile responses to K, noradrenaline (NA) and Ba were investigated in relation to Ca. Removal of Na from BS by replacing NaCl with LiCl accelerated the release and influx of Ca in a short time but inhibited both 40 min later. Increase of Na in BS inhibited both the Ca influx and the Ca release from the storage site of loosely-bound Ca without affecting that of tightly-bound Ca. Evidence was obtained suggesting that Na in BS plays an important role in the uptake of intracellular Ca to the storage site. Removal of K accelerated the release and the influx of Ca in a short time but inhibited both after a long time. Data obtained suggested that Na increase or K removal inhibited the binding of NA to the adrenergic receptor. A single application of high concentrations of K (followed by washout) to the normal BS was markedly effective in restoring the preparation from its decreased contractile responses to NA or Ba following a long exposure to the Na (-), Ca (-) or the K (-), Ca (-) BS. It was suggested that this restoring effect of K is due to excitation of the cell membrane and repletion of the depleted storage site of Ca.
