Extracellular Calcium and Vascular Responses After Forearm Ischemia

Abstract

Background-The myogenic response is a phenomenon in which blood vessels respond to increases and decreases in transmural pressure with constriction and dilation, respectively. Despite intense investigation into the signaling mechanisms underlying this response, the precise mechanisms remain unclear. It has been suggested that the myogenic response occurs when pressure or stretch evokes increases in vessel wall tension that results in vessel smooth muscle cell depolarization. This causes Ca 2ϩ entry through voltage-gated Ca 2ϩ channels. Of note, in vitro studies demonstrate that the magnitude of the myogenic response is dependent on the extracellular Ca 2ϩ . We tested the hypothesis that in conscious humans, physiological changes in extracellular Ca 2ϩ concentrations would be an important determinant of the myogenic response. Methods and Results-Venous blood ionized calcium was used as an index of interstitial calcium and was measured 5, 15, and then every 15 seconds for 75 seconds, then every 30 seconds for 90 seconds, then finally at the 300-second mark. Forearm blood pressure and flow velocity were determined after 10 minutes of forearm ischemia. We found that the rate of change in serum calcium levels varied as a function of transmural pressure (rϭ0.96). Moreover, the calcium concentration was inversely proportional to forearm blood velocity (rϭ0.99). Conclusions-We

Arterial Stiffness Alterations during Hemodialysis: The Role of Dialysate Calcium

“…Arterial tone was calculated as the reciprocal of the oscillatory compliance C 2 . The intradialytic inhibition of sarcoendoplasmic reticulum Ca 2+ -ATPase activity by 64% and the reduction in intracellular stored calcium by 35% noted in the study, in accordance with previous observations [24], provide a reasonable explanation for the vasoconstrictive effects of increased extracellular calcium. In support of this, the increase in artery tone and reduction in sarcoendoplasmic reticulum Ca 2+ -ATPase activity were reversed in 5 HD patients treated with an LdCa of 1.0 mmol/l.…”

Sustained increase of extracellular calcium concentration causes arterial vasoconstriction in humans

“…When extracellular calcium was increased the vessel diameter at a given transmural pressure was reduced, indicating increased myogenic tone in the presence of higher calcium concentrations [28]. In a recent study [6] extracellular calcium was shown to play an important role in mediating the effects of transmural pressure by acting on the myogenic response in humans. In that study an acute increase in transmural pressure raised extracellular calcium and this in turn caused an increase in arterial tone [6].…”

“…In a recent study [6] extracellular calcium was shown to play an important role in mediating the effects of transmural pressure by acting on the myogenic response in humans. In that study an acute increase in transmural pressure raised extracellular calcium and this in turn caused an increase in arterial tone [6].…”

“…Additional experimental data indicated that an acute increase in the extracellular calcium concentration increased systolic blood pressure [5]. A recent study [6] reported that the acute increase in extracellular calcium constitutes an important component of the myogenic vascular response; the vasoconstriction after an increase in transmural pressure was mediated by an increase in the extracellular calcium concentration. The purpose of the present study was to investigate whether a sustained increase in the extracellular calcium concentration was an important determinant of vasoconstriction in humans.…”

Another dimension to calcium signaling: a look at extracellular calcium

“…Xiong et al recently provided evidence that ASIC1a is the key link between ischemia, acidosis and the injurious effects of ischemia in the brain, owing to the influx of toxic levels of Ca 2+ into the cells during activation of the proton-gated channel (Xiong et al, 2004). Note that ischemia might be a condition under which derangements in extracellular [Ca 2+ ], as well as interstitial pH, also occur (Imadojemu et al, 2004).…”