Effects of Added or Substituted Potassium Ion on 45Ca Movements in Rabbit Aortic Smooth Muscle
The effects of elevated potassium ion (K+) concentration on radioactive calcium (45Ca) movements and distribution were investigated in media-intimal strips prepared from rabbit aortic smooth muscle. 45Ca uptake was measured in either normal (1.5 mM Ca2+) or low-Ca (0.1 mM Ca2+) solutions. In low-Ca solutions, elevating the K+ concentration either by substituting equimolar (165.4 mM) K+ for sodium (Na+) (substituted-K solution) or by increasing K+ concentration to 80 mM (added-K solution) increased the 45Ca uptake. Exposure of the muscle strips to high K+ concentrations during washout of 45Ca decreased the 45Ca 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 45Ca 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 (Sr2+) plus 45Ca prevented this decrease in 45Ca efflux. It would appear that the 45Ca affected by high K+ concentrations is at Sr-sensitive sites which are inaccessible to EDTA. If 45Ca at these sites contributes directly to 45Ca efflux, a shift of some of this 45Ca to less superficial cellular sites might be responsible for the decreased efflux of 45Ca observed in the presence of increased K+ concentration.
- Received April 10, 1972.
- Accepted September 11, 1972.
- © 1972 American Heart Association, Inc.