Regulation of arterial diameter and wall [Ca²⁺] in cerebral arteries of rat by membrane potential and intravascular pressure

Abstract

The regulation of intracellular [Ca2+] in the smooth muscle cells in the wall of small pressurized cerebral arteries (100‐200 μm) of rat was studied using simultaneous digital fluorescence video imaging of arterial diameter and wall [Ca2+], combined with microelectrode measurements of arterial membrane potential. Elevation of intravascular pressure (from 10 to 100 mmHg) caused a membrane depolarization from ‐63 ± 1 to ‐36 ± 2 mV, increased arterial wall [Ca2+] from 119 ± 10 to 245 ± 9 nM, and constricted the arteries from 208 ± 10 μm (fully dilated, Ca2+ free) to 116 ± 7 μm or by 45 % (‘myogenic tone’). Pressure‐induced increases in arterial wall [Ca2+] and vasoconstriction were blocked by inhibitors of voltage‐dependent Ca2+ channels (diltiazem and nisoldipine) or to the same extent by removal of external Ca2+. At a steady pressure (i.e. under isobaric conditions at 60 mmHg), the membrane potential was stable at ‐45 ± 1 mV, intracellular [Ca2+] was 190 ± 10 nM, and arteries were constricted by 41 % (to 115 ± 7 μm from 196 ± 8 μm fully dilated). Under this condition of ‐45 ± 5 mV at 60 mmHg, the voltage sensitivity of wall [Ca2+] and diameter were 7.5 nM mV−1 and 7.5 μm mV−1, respectively, resulting in a Ca2+ sensitivity of diameter of 1 μm nM−1. Membrane potential depolarization from ‐58 to ‐23 mV caused pressurized arteries (to 60 mmHg) to constrict over their entire working range, i.e. from maximally dilated to constricted. This depolarization was associated with an elevation of arterial wall [Ca2+] from 124 ± 7 to 347 ± 12 nM. These increases in arterial wall [Ca2+] and vasoconstriction were blocked by L‐type voltage‐dependent Ca2+ channel inhibitors. The relationship between arterial wall [Ca2+] and membrane potential was not significantly different under isobaric (60 mmHg) and non‐isobaric conditions (10‐100 mmHg), suggesting that intravascular pressure regulates arterial wall [Ca2+] through changes in membrane potential. The results are consistent with the idea that intravascular pressure causes membrane potential depolarization, which opens voltage‐dependent Ca2+ channels, acting as ‘voltage sensors’, thus increasing Ca2+ entry and arterial wall [Ca2+], which leads to vasoconstriction.

Bioelectric impact of pathological angiogenesis on vascular function

“…A caveat is that the retinal vasculature was not internally perfused, because it is not currently feasible to obtain patch-clamp recordings from pressurized arterioles within ex vivo or in vivo retinas. Given that luminal pressurization is known to cause vascular depolarization (24,25), it is likely that the membrane potentials measured in our study are higher than those in vivo. However, the difference in voltage is likely modest, because the small retinal arterioles (<20 μm outer diameter) sampled in our study have a reported internal pressure of ∼30 mm Hg in vivo (26), which causes a depolarization of only ∼10 mV as indicated in analysis of nonocular vessels (25).…”

Intravascular pressure-evoked changes in intracellular calcium [Ca2+]i and tone in rat mesenteric and rabbit cerebral arteries in vitro

“…Similar observations have recently been reported in rat mesenteric 12 and rat cerebral arteries. 13 In the latter study increased intravascular pressure was associated with membrane depolarization from −63 mV at 10 mm Hg to −36 mV at 100 mm Hg. This pressureinduced depolarization was proposed to be responsible for L-type calcium channel opening and Ca 2+ influx, thereby accounting for the increase in tone.…”

Activation of Ca2+‐activated Cl− channel ANO1 by localized Ca2+ signals

“…2005; Bulley & Jaggar, 2014). However, physiological activation of ANO1‐mediated CaCCs in smooth muscle is likely to depend on co‐localized Ca 2+ signals since Ca 2+ sensitivity of ANO1 at physiologically relevant voltages is lower than the physiological range of global [Ca 2+ ] i in smooth muscle cells (Knot & Nelson, 1998; Bulley et al . 2012).…”