title: Role of L-type calcium channels in altered microvascular responses to propofol in hypertension.
abstract: BACKGROUND
  Propofol acts as an L-type calcium channel (LTCC) antagonist to decrease peripheral resistance and initiate hypotension. This study investigated LTCC sensitivity/expression in hypertension and the role of LTCCs in exaggerated hypotension to propofol in this situation.
  
  
  METHODS
  Age-matched 12- to 15-week-old normotensive rats [male Wistar Kyoto (WKY)] and spontaneously hypertensive rats (SHR) were used. Propofol (10 mg kg(-1), 10-50 mg kg(-1) h(-1) i.v.) was administered and the mesenteric microcirculation (<70 µm) observed with fluorescent in vivo microscopy using fluorescein isothiocyanate-conjugated bovine serum albumin (100 mg kg(-1) i.v.). Western blotting was used to measure tissue expression of the α(1C) LTCC subtype. Pressure myography was used to assess isolated mesenteric arterioles (<350 µm) in response to BAYK8644 (0.1 nM-1 µM), a specific LTCC channel agonist.
  
  
  RESULTS
  Propofol dilated isolated arterioles {336.6 µM [mean (sd) change 16.2 (5.8)%]}. However, constriction to BAYK8644 was reduced at this concentration of propofol [EC(50)=8.3 (0.1) log mol(-1)] compared with controls [7.4 (0.1) log mol(-1), P<0.05], suggesting that propofol inhibited LTCCs. The sensitivity of LTCCs increased during hypertension, as in vivo there was a greater increase in mean arterial pressure (MAP) to BAYK8644 [10 µg kg(-1), WKY: 59.5 (9.3)%; SHR: 97.7 (6.3)%, P<0.05] with exaggerated constriction of arterioles [10 µg kg(-1), WKY: 9.1 (2.5)%; SHR: 19.1 (2.6)%, P<0.05]. Propofol also decreased MAP in SHR over time (P<0.05), but remained unchanged in WKY. Using western blotting, expression of α(1C) was greater in SHR compared with WKY (P<0.05).
  
  
  CONCLUSIONS
  Propofol acts via LTCC channels, with increased channel expression and sensitivity in genetically hypertensive rats. We suggest that increased sensitivity and expression of LTCCs may be a mechanism for exaggerated hypertension during propofol anaesthesia.
authors.affiliation: Microcirculation Research Group, Faculty of Medicine, Dentistry and Health, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, UK.
authors.forename: B K
authors.initials: BK
authors.lastname: Lawton
authors.forename: N J
authors.initials: NJ
authors.lastname: Brown
authors.forename: C S
authors.initials: CS
authors.lastname: Reilly
authors.forename: Z L S
authors.initials: ZL
authors.lastname: Brookes
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D055806:Microvessels / Q000187:drug effects* / Q000502:physiology; D015742:Propofol / Q000494:pharmacology*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013152:Splanchnic Circulation / Q000187:drug effects
chemical_list: D018686:Anesthetics, Intravenous; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D015742:Propofol