Potassium-induced relaxation of arteries in hypertension: modulation by extracellular calcium.
Smooth muscle relaxation due to activation of Na+-K+-adenosinetriphosphatase (ATPase) (K+ relaxation) was studied in isolated tail arteries from stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rats. Exposure to K+ (7 mM) relaxed a norepinephrine (1 microM) contraction induced in K+-free physiological salt solution (PSS) by 46 +/- 3% in WKY and by 81 +/- 3% in SHRSP. Incubation with monensin (10 microM) augmented the K+-relaxation in WKY to 61 +/- 5%. Incubation with amiloride (10 microM) or with low-Na+ (10 mM) PSS attenuated the K+ relaxation in SHRSP to 34 +/- 3 and 5 +/- 2%, respectively. Incubation with high-Ca2+ (6.6 mM) PSS attenuated the K+ relaxation in WKY to 25 +/- 3% but resulted in only a slight decrease in the relaxation in SHRSP (to 73 +/- 2%). We conclude 1) that a greater Na+ leakiness of the plasma membrane in SHRSP than in WKY while the Na+ pump is inactive in K+-free PSS can explain the greater relaxation observed when the Na+ pump is reactivated and 2) that the Na+ leakiness of the membrane is more attenuated by Ca2+ in the WKY than in the SHRSP. We hypothesize that this Ca2+ effect reflects a normally large amount of this ion that can be bound to and thereby stabilize the membrane of the WKY, decreasing its permeability to Na+. The membrane of the SHRSP is deficient in its Ca2+-binding sites. Hence the added Ca2+ does not further stabilize its membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
Rinaldi
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G
Department of Physiology, University of Michigan, Ann Arbor 48109.
Bohr
D F
DF
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D002118:Calcium / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008985:Monensin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D000584:Amiloride; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine