PC-PLC/sphingomyelin synthase activity plays a central role in the development of myogenic tone in murine resistance arteries

Abstract

Myogenic tone is an intrinsic property of the vasculature that contributes to blood pressure control and tissue perfusion. Earlier investigations assigned a key role in myogenic tone to phospholipase C (PLC) and its products, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Here, we used the PLC inhibitor, U-73122, and two other, specific inhibitors of PLC subtypes (PI-PLC and PC-PLC) to delineate the role of PLC in myogenic tone of pressurized murine mesenteric arteries. U-73122 inhibited depolarization-induced contractions (high external K(+) concentration), thus confirming reports of nonspecific actions of U-73122 and its limited utility for studies of myogenic tone. Edelfosine, a specific inhibitor of PI-PLC, did not affect depolarization-induced contractions but modulated myogenic tone. Because PI-PLC produces IP3, we investigated the effect of blocking IP3 receptor-mediated Ca(2+) release on myogenic tone. Incubation of arteries with xestospongin C did not affect tone, consistent with the virtual absence of Ca(2+) waves in arteries with myogenic tone. D-609, an inhibitor of PC-PLC and sphingomyelin synthase, strongly inhibited myogenic tone and had no effect on depolarization-induced contraction. D-609 appeared to act by lowering cytoplasmic Ca(2+) concentration to levels below those that activate contraction. Importantly, incubation of pressurized arteries with a membrane-permeable analog of DAG induced vasoconstriction. The results therefore mandate a reexamination of the signaling pathways activated by the Bayliss mechanism. Our results suggest that PI-PLC and IP3 are not required in maintaining myogenic tone, but DAG, produced by PC-PLC and/or SM synthase, is likely through multiple mechanisms to increase Ca(2+) entry and promote vasoconstriction.

Central Role of P2Y 6 UDP Receptor in Arteriolar Myogenic Tone

“…Unlike P2ry6 −/− animals, P2ry2 −/− mice did not display altered MT (Figure IX in the online-only Data Supplement) highlighting a nonredundant role of P2Y 6 receptor in MT where intracellular calcium increase is minimally involved. 21 …”

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

“…In contrast, studies in fourth-order murine mesenteric arteries found no role for IP 3 and IP 3 Rs in myogenic tone (966). Instead, they propose that PLC hydrolyzes phosphatidylcholine to produce DAG that is essential for myogenic tone in this murine resistance artery (966). …”

“…In murine mesenteric resistance arteries it was also shown that block of IP 3 Rs with xestospongin C had no effect on myogenic tone (966). Thus, in these vessels IP 3 Rs do appear to contribute to myogenic tone.…”

Calcium Channels in Vascular Smooth Muscle

“…Pharmacological inhibition of IP 3 R can be achieved with the application of widely used agents such as 2-APB and xestospongin C. IP 3 R inhibition may have distinct effects on vascular reactivity. For instance, in mouse mesenteric arteries, IP 3 R inhibition with xestospongin C did not affect the myogenic tone, but did prevent the phenylephrine-induced vasoconstriction (Mauban, Zacharia, Fairfax, & Wier, 2015). IP 3 R activity in VSM can be modulated by [Ca 2+ ] i , luminal SR Ca 2+ load, ATP, several protein kinases (e.g., PKA, PKG), regulatory proteins (e.g., RACK, FKBP12), reactive oxygen species (ROS), and pH (Bezprozvanny, Watras, & Ehrlich, 1991; Iino, 1990; Narayanan et al, 2012).…”