Enhanced myogenic response in resistance small arteries from spontaneously hypertensive rats: relationship to the voltage-dependent calcium channel

To characterize the myogenic response during the development of hypertension, we evaluated the myogenic response of small arteries isolated from the cremaster muscle of spontaneously hypertensive rats (SHR) aged 4–5 and 7–8 weeks, as compared with age-matched Wistar-Kyoto rats (WKY), using an in vitro system. The myogenic response of SHR aged 7–8 weeks (but not those aged 4–5 weeks) significantly exceeded that of WKY. Measurement of intracellular levels of free calcium ([Ca2+]i) in small arteries of the 7–8-week-old SHR and WKY loaded with a calcium-sensitive dye showed that the increase in [Ca2+]i in SHR was significantly greater than that in WKY during the myogenic response. The inhibitory effects of nitrendipine on the increased myogenic response and [Ca2+]i were greater in SHR. Thus, the myogenic response was enhanced in SHR and may be explained in part by an increase in Ca2+ entry through the voltage-dependent calcium channel (VDCC). The myogenic response and Ca2+ entry through the VDCC may be increased in association with the elevation of blood pressure.