Effects of angiotensin, catecholamines and cyclic AMP on calcium storage in aortic microsomes.

Abstract

1. The binding of calcium observed in microsomal membranes derived from the intimal-medial layer of rabbit aorta was specifically increased by the magnesium salt of adenosine triphosphate (Mg-ATP). This calcium uptake was inhibited by potassium and sodium.2. Angiotensin II, both in the presence and in the absence of Mg-ATP, reduced the binding of calcium and increased the release of membrane-incorporated calcium. These effects were dose-dependent. Analogues of angiotensin II devoid of intrinsic activity, failed to alter the release of calcium.3. Dibutyryl-cyclic AMP increased the binding of calcium and reduced the rate of its release. The maximal effect was observed at the concentration of 10(-5)M.4. (-)-Noradrenaline reduced the binding of calcium; this effect was inhibited by phenoxybenzamine. Conversely, adrenaline like cyclic AMP, increased the calcium binding; the effect of adrenaline was suppressed by a beta-adrenoceptor blocking agent.5. These observations demonstrate the existence of membranes in rabbit aorta capable of storing calcium. Excitatory drugs seem to affect directly and specifically the binding and release of calcium in these membranes.