Vascular effects of potassium cardioplegic solutions

Experiments have been performed on isolated human umbilical and sheep coronary arteries, studying the effects of increasing potassium concentration in steps from 10 to 160 mM. Comparative studies were also done on rat-heart papillary-muscle preparations. The results revealed a dose-dependent increase in smooth muscle tone of the blood vessels. Maximal contraction was reached at 80 mM K+. Papillary-muscle preparations showed a dose-dependent decrease in contractile activity. Complete stoppage of contractile activity was observed at 30 mM K+. The corresponding increase in the vascular smooth muscle tone at 30 mM K+ was 10-25%, showing that vascular smooth muscle cells are less easily affected by increasing K+ than the heart. Further confirmation of the results were obtained by exposing the preparations (papillary muscle and arteries) to a locally-developed depolarizing K+-cardioplegic solution.