Characteristics of the Norepinephrine-Sensitive Ca²⁺ Store in Vascular Smooth Muscle

Abstract

A comparison was made between the properties of the norepinephrine- and caffeine-sensitive Ca²⁺ store in both intact and skinned smooth muscle of the rabbit mesenteric artery. After a first application of 10^-5M norepinephrine, reapplication of norepinephrine did not induce a second contraction in Ca²⁺-free medium. However, following this sequence 25 mM caffeine still induced a large contraction. The rates of Ca²⁺ leakage and Ca²⁺ filling of the norepinephrine-sensitive store were much faster than those of the caffeine-sensitive one. The amplitude of the norepinephrine-induced contraction in Ca²⁺-free medium also depended on the amount of Ca²⁺ present in the caffeine-sensitive store. In the saponin-treated skinned muscle caffeine induced a Ca²⁺ release only after loading with Ca²⁺, whereas norepinephrine was unable to induce Ca²⁺ release in the skinned preparation even after loading with Ca²⁺. The release of Ca²⁺ from the caffeine-sensitive store could be activated by Ca²⁺ itself when the skinned muscle was loaded with Ca²⁺ above 10^-6M. These results suggest that the norepinephrine-sensitive Ca²⁺ store is distinct from a large fraction of the caffeine-sensitive one, and that the norepinephrine-sensitive store is close to the cell membrane. In vascular smooth muscle, under physiological conditions, Ca²⁺ released from the norepinephrine-sensitive store by norepinephrine may induce Ca²⁺ release from the caffeine-sensitive Ca²⁺ store which may be comprised of the sarcoplasmic reticulum.

A voltage-dependent noradrenaline-sensitive intracellular calcium store in smooth muscle cells of the guinea-pig aorta

“…Consistent with these ca2+ eflux results, many contractile studies on vascular smooth muscle (Itoh et ai, 1983;Leijten and van Breemen, 1984;Saida and van Breemen. 1984) suggest that the NA-sensitive store and CAF-sensitive store overlaps.…”

Effect of cromakalim on contractions in rabbit isolated renal artery in the presence and absence of extracellular Ca2+

“…It has been shown that the store released by the two agents is identical (Itoh et al, 1982);Leijten & van Breemen, 1984). However, others suggest that the overlap of stores is not complete (Deth & Casteels, 1977;Saida & van Breemen, 1984). It is, however, evident that noradrenaline and caffeine do not release Ca2+ by the same mechanism.…”

Rat arterial smooth muscle devoid of ryanodine receptor function: effects on cellular Ca2+ handling

“…The acute eect of Ry is to open its receptor/channel and thereby to empty Ca 2+ stores, precluding SR accumulation of Ca 2+ . Since the Ry receptor and the IP 3 receptor appear to be located to the same stores, or to rapidly communicating stores (Saida & van Breemen, 1984;Komori et al, 1995), Ry treatment will also abolish responses to agents acting through IP 3 . Inhibitors of the Ry receptor, such as ruthenium red, procaine and Mg 2+ all have additional eects on muscle (Crompton et al, 1983;Benham et al, 1985).…”