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  • Title: [Norepinephrine-sensitive calcium pools in tail arteries of normotensive and spontaneously hypertensive rats: effects of ryanodine and caffeine].
    Author: Rinaldi GJ.
    Journal: Acta Physiol Pharmacol Latinoam; 1990; 40(3):339-55. PubMed ID: 2094167.
    Abstract:
    The effects of Ryanodine (RY) and Caffeine (CF) on the norepinephrine (NE)-induced contraction were studied in tail artery rings from spontaneously hypertensive rats (SHR) and normotensive, Wistar Kyoto rats (WKY). The NE-sensitive intracellular store of calcium was completely depleted by NE (1 microM) in calcium-free physiological salt solution (Ca = 0-PSS), and accounted for approximately 40% of the total response to NE in regular PSS (Ca = 1.6 mM). However, only 60% of the NE-releasable store was utilized for the full contraction in PSS. Re-exposure to PSS completely replenished the NE-releasable store in 10 minutes. Over twice as much calcium appeared to be taken up by the SHR as by the WKY arteries in these conditions. RY prevented the refilling of the NE-sensitive calcium store in both SHR and WKY, without releasing calcium from the store and without affecting the influx of calcium through membrane pathways. CF also prevented the refilling of the NE-sensitive calcium store, but did release calcium from it. It can be concluded that: 1) Whereas the main action of RY on rat tail artery seems to be the inhibition of calcium uptake by the sarcoplasmic reticulum (SR), CF has several actions: a) inhibition of calcium uptake by the SR, b) release of calcium from the SR, and c) opening of calcium channels in the plasma membrane of the smooth muscle cell. 2) In SHR, but not in WKY, the loss of calcium from the membrane in Ca = 0-PSS renders it more permeable to calcium, permitting an enhanced calcium uptake during subsequent exposure to PSS.
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