Contractile Responses of Isolated Rabbit Aortae to Transmural Stimulation as Affected by Calcium, Strontium, Sodium and Ouabain

Abstract

There are a number of reports describing that not only in visceral (1-3) but also vascular smooth muscles (4-6) Ca<SUP>++</SUP> may be the agent linking membrane excitation to contraction.Increasing [Ca<SUP>++</SUP>]<SUB>0</SUB> may either stimulate (7,8) ranging from 0 to 4.4 mM (13).<BR> It seems likely that Sr<SUP>++</SUP> can substitute for Ca<SUP>++</SUP> in the contractile mechanism of skeletal, cardiac and smooth muscles (14-18) and in the release of the neurohumoral trans mitter from sympathetic nerve terminals (18). It appears that Na<SUP>+</SUP> acts through an antago nism to Ca<SUP>++</SUP> on muscular contractility (4, 19) and uptake of noradrenaline by sympathetic nerves (20). Ouabain is known to increase the exchangeable Ca<SUP>++</SUP> fraction (21 , 22), which would be expected to participate in increased contractility.<BR>The present study was an investigation into the effects of ions and drugs that interact with Ca<SUP>++</SUP> on the resting tension of the vascular smooth muscle and on its contractile res ponse to electrical transmural stimulation and exogenous noradrenaline. METHODSAlbino rabbits of both sexes, weighing 1.8 to 2.2 kg, were used. Under ether anesthesia the animals were sacrificed by bleeding from both common carotid arteries . The ascending aorta was rapidly removed and cut into spiral strips. The strips were held vertically under a resting tension of 2 g in the muscle bath of 100 ml capacity containing the nutrient solution. The solution was maintained at 37.1 0.5-C and gassed with a mixture of 95""0 / 0, and 5(" CO,. Constituents of the solution were as follows (mM): Na+, 162.1 ; K+, 5.4; Ca", 21.21; 157"0; HCO,14,9; dextrose, 5.6. Osmotic adjustment was not made when [Ca++]

Adrenergic Potentiation by Angiotensin II in Isolated Canine Cutaneous Arteries: Effect of Bathing Media and Calcium

“…Raising the calcium in the medium to 5 mM increased the responses to field stimulation and norepinephrine. Others have indicated that increasing calcium above the normal range augments adrenergic transmitter release [6,8], whereas T oda [10] found no effect on the responses to transmural stimulation. In our experiments the responses to both field stimulation and norepinephrine were potentiated by raising calcium concentration, which suggests that a postsynaptic effect of cal cium was involved, yet a presynaptic influence cannot be totally ruled out.…”

The Role of Bound Calcium in Super‐sensitivityinduced by Cocaine

“…Potentiation of the strontium-induced contraction by cocaine in a calcium-free solution Strontium has been shown to cause contraction of smooth muscle (Daniel, 1963) and can substitute for calcium in the contraction of smooth muscle (Daniel, 1965;Hudgins, 1969;Toda, 1972). Experiments were done to see if strontium would contract the isolated spleen strip in the absence of extracellular calcium, and whether cocaine would potentiate this response.…”

“…Strontium can substitute for calcium in the contraction of smooth muscle (Sperelakis, 1962;Daniel, 1963;Bohr, 1964;Hudgins, 1969), possibly by displacing bound intracellular calcium (Daniel, 1965;Toda, 1972). Our experiments where pretreatment of the cat with reserpine did not reduce the contraction caused by strontium in spleen strips bathed in calcium-free solution indicate that the contraction was not due to the release of stored noradrenaline.…”

Ouabain‐Induced Coronary Vasoconstriction In Cats Is Not Neurally Mediated

“…The mechanism appears to include both direct vasoconstriction and a neurally mediated effect 7 . Direct vasoconstriction of blood vessels by digitalis has been demonstrated in excised strips of arteries, veins 9–14 and aortas 15,16 …”