[Spontaneous rhythmic contractions of human placental vessels: is it an evidence for a physiological pacemaker in blood vessels?].
BACKGROUND
Placental vessels are not innervated. Therefore the vasomotor activity and vascular tone is not regulated by the nervous system.


OBJECTIVE
To assess the existence of pacemaker mechanisms related to rhythmic motor activity of blood vessels.


METHODS
Isometric contractions of rings from umbilical and chorionic vessels of term human placentas were monitored.


RESULTS
Recordings of the circular layer of chorionic and umbilical vessels revealed rhythmic spontaneous contractions with a frequency of 1.4 +/- 0.05 cycles/min, the duration of each cycle was 42.8 +/- 0.24 s (n = 12). The amplitude of contractions was larger in veins than in arteries, predominating in umbilical vein biopsies, proximal to the fetus. Both the frequency and the amplitude of contractions were relatively constant during the first 30 min. However, after an hour, the frequency declined while the amplitude increased. The absence of the endothelium neither modified the frequency nor the amplitude of the rhythmic activity. Blockage of voltage dependent sodium channels or calcium channels did not alter the frequency of spontaneous contractions, although their magnitude was reduced. Glibenclamide, an ATP-dependent K+ channel blocker or the blockade of gap junctions ablated the frequency and amplitude of spontaneous contractions.


CONCLUSIONS
We propose that rhythmic contractions are triggered by pacemaker cells located in the circular layer of the smooth muscle of blood vessels and spread via gap junctions; they likely contribute to the control of blood flow.
Huidobro-Toro
J P
JP
Instituto Milenio de Biología Fundamental y Aplicada (MIFAB), Departamentos de Fisiología, Cardiología y Cirugía Digestiva, Facultad de Ciencias Biológicas y Facultad de Medicina, Pontificia Universidad Católica de Chile.
González
R
R
Varas
J A
JA
Rahmer
A
A
González
R
R
D001683:Biological Clocks; D001808:Blood Vessels / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002823:Chorion / Q000098:blood supply / Q000502:physiology; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000166:cytology; D005260:Female; D017629:Gap Junctions / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D010920:Placenta / Q000098:blood supply* / Q000166:cytology; D015222:Sodium Channels / Q000502:physiology; D014471:Umbilical Veins / Q000502:physiology*
D015220:Calcium Channels; D015222:Sodium Channels
Actividad rítmica espontánea en vasos de placenta humana: un marcapaso fisiológico en los vasos sanguíneos?