Calcium exchange in vascular smooth muscle, action of noradrenaline and lanthanum.

Abstract

SUMMARY1. The Na, K, Ca and Mg content and the 45Ca uptake and loss were determined in rat aortae incubated in physiological solution or in solution containing LaCl3 instead of CaCl2.2. Aortae washed in La-solution contained less Ca and Na than controls in physiological solution, the K content was not modified and the Mg content was slightly decreased. 4. Noradrenaline increased the rate of uptake of 45Ca into the Ca fraction resistant to displacement by La. This increase was dose dependent, a response of 50 % of the maximum being produced by 2 x 10-8 noradrenaline as for the contraction. In the presence of phentolamine, the doseeffect curves for the action of noradrenaline on 45Ca uptake were displaced in a manner characteristic of competitive antagonism. The pA2 for phentolamine was 7-8.5. In physiological solution, the rate of loss of 45Ca, from the Ca fraction resistant to displacement by La, was increased by noradrenaline the ED50 was 2 x 104M, and the effect was abolished by phentolamine.6. In view of the similarity of phentolamine pA2 estimated by measuring noradrenaline sensitive 45Ca uptake or noradrenaline evoked contraction, it is likely that the activation of ac-adrenergic receptors is responsible for both effects.

Effects of Bay K 8644 on 45Ca uptake and efflux and on contraction in the rabbit aorta

“…The aorta was cleared of adherent tissues and crosssectioned into rings. 45Ca uptake 45Ca uptake in rabbit aorta was conducted using a modified 'Lanthanum method', where a low temperature (0.5°C) and incubation with a high La3" concentration (50 mM) was chosen (Godfraind, 1976; ) The Macmillan Press Ltd 1986 Deth, 1978;Hay & Wadsworth, 1984 Packard Tri-Carb 460 CD scintillation counter and the cellular 45Ca content calculated. 45Ca efflux 45Ca efflux was measured by a superfusion method using paired preparations which were run simultaneously.…”

Stimulation and Inhibition of the Sodium Pump by Cardioactive Steroids in Relation to Their Binding Sites and Their Inotropic Effect on Guinea‐pig Isolated Atria

“…The procedure was similar to that followed with smooth muscle (Godfraind, 1976 H202 (30 vol). This solution was heated at 60°C for 30 min and after cooling was added to 10 ml of a scintillation solution (bis MSB 0.5 g, PPO 4 g, Triton X100 350 ml, toluene 650 ml).…”

Increase by oestrogen of calcium entry and calcium channel density in uterine smooth muscle

“…Lanthanum, which has been shown to displace extracellular calcium while having no effect on intracellular calcium was used to remove 4"Ca in the extracellular space (Van Breemen et al, 1972;Godfraind, 1976). The method by which only the net calcium influx was measured in uterine tissue has been described in detail previously (Batra, 1985).…”