Effects of added or substituted potassium ion on 45 Ca movements in rabbit aortic smooth muscle.

The effects of elevated potassium ion (K) concentration on radioactive calcium (Ca) movements and distribution were investigated in media-intimal strips prepared from rabbit aortic smooth muscle. Ca uptake was measured in either normal (1.5 rriM Ca ) or low-Ca (0.1 mM Ca ) solutions. In low-Ca solutions, elevating the K concentration either by substituting equimolar (165.4 IHM) K for sodium (Na) (substituted-K solution) or by increasing K concentration to 80 mM (added-K solution) increased the Ca uptake. Exposure of the muscle strips to high K concentrations during washout of Ca decreased the Ca efflux into either zero-Ca or low-Ca bathing solutions. Moreover, increased K concentration elicited its effects in the presence or the absence of Na + . The decrease in Ca efflux induced by substituted-K solution was also obtained in the presence of ethylenediaminetetraacetic acid (EDTA), but prior incubation of muscles with 1.5 mM strontium (Sr) plus Ca prevented this decrease in Ca efflux. It would appear that the Ca affected by high K concentrations is at Sr-sensitive sites which are inaccessible to EDTA. If Ca at these sites contributes directly to Ca efflux, a shift of some of this Ca to less superficial cellular sites might be responsible for the decreased efflux of Ca observed in the presence of increased K concentration.