Cytosolic Free Calcium of Aorta in Hypertensive Rats Chronic Inhibition of Angiotensin Converting Enzyme

Cytosolic free calcium concentration ([Ca+t) and muscle tension were simultaneously measured in aortic tissue isolated from spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto (WKY) rats, and SHR chronically treated with a novel angiotensin converting enzyme inhibitor, CS-622. In the presence of 2.5 mM Ca in the bathing solution, aortic [Ca], measured with fura-2 was higher in SHR than in WKY rats, and it was almost the same in CS-622-treated SHR and untreated WKY rats. Increase of external Ca concentration from zero to 2.5 mM elicited a contraction in SHR aortas but not in aortas from both CS-622-treated SHR and untreated WKY rats. When the aortas were contracted by 60 mM K+, however, [Ca], as well as developed tension was similar in the three groups. CGP-28392 (10 M), a Ca channel activator, induced a rhythmic activity superimposed on a gradual increase of [Ca], and tension in SHR aortas but not in the aortas of CS-622-treated SHR or untreated WKY rats. Nicardipine (10∼7 M) decreased the resting [Ca], and the resting tone in SHR aortas, but not in WKY rat aortas. These results suggest that SHR aortas have a higher myogenic tone due to increased [Ca], than WKY rat aortas and that the increased [Ca2+], is attributed to alterations of dihydropyridine-sensitive Ca2+ channels in SHR aortas. Further, the decrease of the vascular tone induced by long-term administration of the angiotensin converting enzyme inhibitor may be due to a reduction of increased [Ca], in SHR.