Figure 2.

Relationships between intravascular pressure, vessel diameter, [Ca²⁺]_i and V_m in pial arteries and parenchymal arterioles. (a) One fundamental difference between vessels of the cerebral circulation is that parenchymal arterioles develop more tone in response to lower intravascular pressure compared to pial arteries. (b) The phenomenon in A is linked to the parenchymal arteriole SM V_m, which is more depolarized in response to lower pressure compared to pial arteries. (c) Increases in [Ca²⁺]_i in response to increasing intravascular pressures are greater in parenchymal arterioles than in pial arteries owing to higher voltage-dependent calcium channel (VDCC) activity caused by the greater degree of SMC cell depolarization, as illustrated in (b). (d) There is no difference in the sensitivity of the SM contractile apparatus to Ca²⁺ between pial arteries and parenchymal arterioles, indicating that the difference in the pressure-constriction relationship between these two types of vessels is due to the difference in SM V_m in response to pressure. Data were re-plotted from ref.⁹ Parenchymal arteriole V_m data were obtained from F. Dabertrand (personal communication) and from Nystoriak et al.⁹ and Hannah et al.¹⁰