title: Electrophysiological properties of rat mesenteric lymphatic vessels and their regulation by stretch.
abstract: BACKGROUND
  In mammals, lymph is propelled centrally primarily via the phasic contractions of collecting lymphatic vessels, known as lymphatic pumping. Electrophysiological studies conducted in guinea pig and sheep mesenteric lymphatic vessels indicate that contractions are initiated in the lymphatic muscle by nifedipine-sensitive action potentials (APs). Lymphatic pumping is highly sensitive to luminal fluid loading and the mechanical properties of this stretch-induced pumping have been consistently studied, in particular in rat mesenteric lymphatic vessels. However, membrane potential (Vm) and the electrophysiological events underlying stretch-induced lymphatic pumping have not been investigated in the rat. The aim of this study was thus to examine the properties of rat mesenteric lymphatic muscle Vm under resting conditions and to assess changes in Vm caused by distension.
  
  
  RESULTS
  Lymphatic muscle Vm was measured with sharp intracellular microelectrodes either in unstretched conditions or under isometric tension provided by a wire-myograph. In unstretched vessels, Vm was -48 ± 2 mV (n=30). APs (amplitude ∼25 mV) were observed at a frequency of ∼8/min and were abolished by nifedipine. Under isometric tension, Vm was less polarized (-36 ± 1 mV, n=23), even at minimum tension. Increase in tension led to increase in contraction strength and contraction/AP frequency, while Vm was slightly hyperpolarized and AP amplitude not markedly altered.
  
  
  CONCLUSIONS
  In our experimental conditions, rat lymphatic muscle has electrophysiological characteristics similar to that in other species. It responds to an increase in isometric tension with an increase in AP frequency, but resting Vm is not significantly affected.
authors.affiliation: 1 Inflammation Research Network and Smooth Muscle Research Group, Snyder Institute for Chronic Diseases, Department of Physiology and Pharmacology, Faculty of Medicine, University of Calgary , Calgary, Alberta, Canada .
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: von der Weid
authors.forename: Stewart
authors.initials: S
authors.lastname: Lee
authors.forename: Mohammad S
authors.initials: MS
authors.lastname: Imtiaz
authors.forename: David C
authors.initials: DC
authors.lastname: Zawieja
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Davis
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D006168:Guinea Pigs; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology*; D042601:Lymphatic Vessels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008643:Mesentery / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009213:Myography; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D046509:Tissue Culture Techniques; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014665:Vasodilator Agents; D009543:Nifedipine