Role of L-type calcium channels in altered microvascular responses to propofol in hypertension.

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. 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. 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). 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.