Contraction and Ca2+-uptake of aortic smooth muscle from Spontaneously Hypertensive Rats

To find out the cellular role to develop hypertension, the characteristics of membrane systems in vascular smooth muscle to regulate the intracellular Ca2+ level were investigated. The differences between Spontaneously Hypertensive Rats (SHR, Okamoto-Aoki) and Kyoto Wistar normotensive rats (KNR) in contractile response and Ca2+ influx in the presence and absence of Ca2+-antagonist (verapamil) were analyzed. (i) Aortic strip could induce rapid tension by serotonin (5HT) and noradrenaline (NA) in Ca2+-free medium but not by K+. (ii) SHR aortic strips developed larger tension than KNR in normal physiological salt solution (PSS). (iii) SHR aortic strips developed tension was more inhibited by verapamil than KNR. (iv) Ca2+ influx in aortic tissue from SHR was smaller than that from KNR, and verapamil inhibited Ca2+ uptake in SHR more greatly than in KNR. These findings suggest that the membrane systems of SHR aortic muscle have an abnormal function