Dual dependence on both Ca2+ and Mg2+ for electrical stability in cells of canine false tendon.
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Action Potentials↗
Biomedical subjects
W T Woods
Publications and source records attributed to W T Woods.
Electrophysiological effects of magnesium on cells in the canine sinus node and false tendon.
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Animals↗
Progressive postnatal changes in sinus node response to atropine and propranolol.
Postnatal development of autonomic control of heart rate was evaluated in the sinus nodes of isolated, perfused right atria obtained from 21 sibling puppies in three different litters between 3 and 11 wk postpartum. Age-related changes in response to autonomic blockade indicated that propranolol administered after atropine had its most profound direct depressive effect on less mature atrial cells. In the youngest sinus nodes the familial antimuscarinic action (increase in sinus rate) of atropine was regularly preceded by a brief period of cholinomimetic action (a marked slowing of sinus rate) in the youngest sinus nodes. These two opposing effects of atropine underwent a developmental change during the 2-mo study. The cholinomimetic action diminished, whereas the antimuscarinic action increased as a function of age.
Aging↗
The effect of papaverine on sodium-potassium adenosine triphosphatase and the ouabain sensitive electrical properties of crayfish nerve.
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Acetylcholinesterase↗
Spontaneous action potentials of cells in the canine sinus node.
Right atria were excised from the hearts of 20 young dogs (15 +/- 5 weeks old) and maintained in vitro in order to perform microelectrode impalements. The atria contracted spontaneously for at least 6 hours at a stable rate of 127/min when they were perfused with Krebs-Ringer bicarbonate solution through the sinus node artery. Cells within a small area near the sinus node artery and between the superior vena cava and right atrium consistently yielded transmembrane potentials typical of pacemaker cells. This area was verified histologically to be the midportion of the sinus node. Electrical characteristics of these sinus node pacemaker cells were: maximum diastolic potential, -56 +/- 7 mV (mean +/- 1 SD); action potential amplitude, 56 +/- 8 mV; overshoot, 0 +/- 2 mV. Smooth transitions from phase 4 to phase 0 were always present. From these experiments we conclude that the excised perfused canine right atrium provides a useful new experimental cardiac preparation because it maintains stable spontaneous activity for many hours in vitro and the sinus node within it is readily accessible for study by intracellular microelectrodes.
Action Potentials↗