Unusual effects of SCN and lyotropic anions on contractility of vascular smooth muscle from female rats

Abstract

Replacement of extracellular chloride ions by thiocyanate anions (SCN-) followed by washout in normal chloride-containing solution produced contractions in isolated rat aortas and portal veins of female rats followed by slow relaxation; these contractions consisted of fast and slow phases. These SCN(-)-induced biphasic contractions were also noted in rat aortas precontracted by 80 mM KCl and 100 microM noradrenaline. No differences were noted between isolated aortic precontracted by 80 mM KCl and 100 microM noradrenaline. No differences were noted between isolated aortic strips versus intact ring preparations. The SCN(-)-induced contractions in both the aorta and portal vein were inhibited markedly by denervation with 6-hydroxydopamine. Use of prazosin, rauwolscine, propranolol, atropine, methysergide, diphenydramine, indomethacin or procaine (10(-3) M) failed to alter the SCN(-)-induced responses. However, use of phentolamine at 10(-5) M, but not at lower concentrations of the drug, resulted in complete inhibition of SCN(-)-induced contractions. Treatment of the vascular tissues with EGTA (5 mM) or incubation in Ca(2+)-free media abolished the SCN(-)-induced contractile responses. Treatment with verapamil (10(-6) M) or washing in Ca(2+)-free Krebs Ringer solution after incubation with SCN(-)-Krebs Ringer selectively inhibited the slow phases of the aortic contractions. Replacement of SCN- anions with other foreign monovalent anions or with sucrose modified the amplitude of the SCN(-)-induced contractions. These foreign anions seemed to follow a relative order of potency similar to that for a lyotropic series of anions, where acetate greater than isethionate greater than chloride greater than bromide greater than nitrate greater than iodide ions.(ABSTRACT TRUNCATED AT 250 WORDS)