Effects of inorganic cations on K +-, 5-hydroxytryptamine- and noradrenaline-induced contractions of the isolated rat jugular vein and aorta

Abstract

We investigated the inhibitory effects of 1 mM of the inorganic cations, La 3+, Cd 2+, Mn 2+, Ni 2+ and Co 2+ on contractions induced by K + (100 mM) and 5-hydroxytryptamine (5-HT, 10 −5 M) in the isolated rat jugular vein and on contractions induced by K + (100 mM), 5-HT (10 −5) and noradrenaline (NA, 10 −5 M) in the rat aorta. In the venous preparation, both K +- and 5-HT-induced Ca 2+ influx could be suppressed completely by all cations studied. In the aorta, the K +-induced Ca 2+ influx was antagonized completely only by Cd 2+. The other cations were less effective and Mn 2+ was completely ineffective. Similarly to that in the venous preparation, the 5-HT-induced Ca 2+ influx in the aorta was abolished by all the cations. A similar picture was found for the NA-induced Ca 2+ influx with the exception of Mn 2+, which antagonized the NA-induced contractions only slightly. Although organic calcium entry blockers (CEBs) (nifedipine, diltiazem, flunarizine and gallopamil) inhibited NA-induced contractions to the same extent as did Mn 2+, a combination of organic CEBs and Mn 2+ abolished the NA-induced Ca 2+ influx completely. Apparently, organic CEBs and Mn 2+ block different components of the NA-induced Ca 2+ influx pathway.