TY - JOUR
T1 - Extracellular calcium and intrinsic tone in the human umbilical artery
AU - Wylam, M. E.
AU - Samsel, R. W.
AU - Schumacker, P. T.
AU - Umans, J. G.
PY - 1993
Y1 - 1993
N2 - Previous in vitro studies of the human umbilical artery (HUA) have suggested that this vessel exhibits significant intrinsic tone, even in the absence of contractile agonists. Other investigators have found that these vessels are unresponsive to nitrovasodilators, suggesting that the guanylate cyclase-mediated relaxation mechanism may not be operative. To clarify these observations, human umbilical cords were obtained at the time of delivery and HUA rings were studied in organ baths. In contrast to other systemic arteries, HUA rings exhibited unstable initial tone in the absence of pharmacologic agonists. This intrinsic tone was augmented when the extracellular ionized calcium concentration was increased and abolished when extracellular calcium was removed. Rings maintained in the presence of extracellular calcium for 1 hr became less responsive to changes in extracellular calcium than did rings maintained in calcium-free buffer. Serotonin produced oscillatory, quantal contractions in the presence of calcium; in the absence of extracellular calcium, it elicited only concentration-dependent graded contractions. In the presence of nifedipine or in the absence of extracellular calcium, nitroglycerin fully relaxed contractions elicited by serotonin. Thus, in HUA, extracellular calcium produces intrinsic tone that diminishes spontaneously with time.
AB - Previous in vitro studies of the human umbilical artery (HUA) have suggested that this vessel exhibits significant intrinsic tone, even in the absence of contractile agonists. Other investigators have found that these vessels are unresponsive to nitrovasodilators, suggesting that the guanylate cyclase-mediated relaxation mechanism may not be operative. To clarify these observations, human umbilical cords were obtained at the time of delivery and HUA rings were studied in organ baths. In contrast to other systemic arteries, HUA rings exhibited unstable initial tone in the absence of pharmacologic agonists. This intrinsic tone was augmented when the extracellular ionized calcium concentration was increased and abolished when extracellular calcium was removed. Rings maintained in the presence of extracellular calcium for 1 hr became less responsive to changes in extracellular calcium than did rings maintained in calcium-free buffer. Serotonin produced oscillatory, quantal contractions in the presence of calcium; in the absence of extracellular calcium, it elicited only concentration-dependent graded contractions. In the presence of nifedipine or in the absence of extracellular calcium, nitroglycerin fully relaxed contractions elicited by serotonin. Thus, in HUA, extracellular calcium produces intrinsic tone that diminishes spontaneously with time.
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M3 - Article
C2 - 8371151
AN - SCOPUS:0027860510
SN - 0022-3565
VL - 266
SP - 1475
EP - 1481
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
IS - 3
ER -