Strontium and Barium as Substitutes for Calcium on Electrical and Mechanical Activity in Rat Portal Vein

Abstract

Sr (above 0.5 mm) and Ba (above 0.25 mm) can maintain spontaneous electrical activity of portal vein in the absence of Ca. This is true also in Na-free solution. An approximately normal pattern of activity with well-defined periods of quiescence is obtained with Sr at lower concentrations than with Ca. Ba causes continuous tetanic spike discharge. Excitation-contraction coupling appears less effective with Sr and Ba than with Ca. These differences can explain the different concentration-effect curves obtained for the three ions with regard to integrated isometric force. The contracture responses of depolarized portal vein induced by Ca, Sr or Ba decreased by 27, 44 and 63 %, respectively, after 30 min in Ca-free solution with 1 mm EGTA. No further decrease occurred after 2 h. The mechanical responses to Sr and Ba appear to be combined effects of liberation of tissue Ca and direct action on the contractile system.