Regulation of Vascular L-type Ca ²⁺ Channels by Phosphatidylinositol 3,4,5-Trisphosphate

Abstract

Abstract-Modulation 6 -8 This mechanism seems to underlie the increased vascular spontaneous tone observed in hypertensive rats. 9 However, how PI3K is able to regulate Ca 2ϩ channels activity remains to be elucidated. 10 Class I PI3Ks are enzymes that selectively phosphorylate the 3Ј-OH position of the PI(4,5)P 2 inositol ring in vivo to generate PI(3,4,5)P 3 , further metabolized by inositol lipid phosphatases to PI(3,4)P 2 . PI(3,4)P 2 and PI(3,4,5)P 3 are absent in resting cells, increase on class I PI3K activation during cellular stimulation, and interact with pleckstrin homology (PH) domains of cellular proteins to transduce signal. Class I PI3Ks have been subclassified according to their structure and mode of activation by cell surface receptors. Class IA PI3Ks are heterodimers composed of a catalytic subunit (the ubiquitous p110␣ or more tissue-restricted p110␤, or p110␦) tightly complexed to a regulatory adapter subunit (p85␣, p85␤, p55, or their splice variants). These regulatory subunits dock the holoenzyme to the membrane through interactions with specific phosphotyrosyl-containing sequences within receptor tyrosine kinases or other membrane-associated proteins. Class IB PI3K is composed of the p110␥ catalytic subunit associated with a p101 regulatory protein. PI3K␥ is specifically stimulated by G␤␥ dimers liberated on G protein-coupled receptor (GPCR) activation. The p110␥ catalytic subunit contains all the structural elements necessary for G␤␥-induced stimulation. The p101 noncatalytic regulatory subunit, which is able to bind lipid substrates, increase p110␥ activity. 11 PI3K␤ is synergistically activated by GPCRs and receptor tyrosine kinases. Like for other class IA enzymes, phosphotyrosyl peptide interaction with the p85 regulatory subunit leads to activation of PI3K␤. However, p110␤ catalytic subunits can be directly activated by membrane-bound ␤␥ dimers. 12 Original

Ryanodine receptor subtype 2 encodes Ca2+ oscillations activated by acetylcholine via the M2 muscarinic receptor/cADP-ribose signalling pathway in duodenum myocytes

“…Permeabilized cells were incubated in the presence of 100 µM NGD+ and the emitted fluorescence was collected with a CoolSnap HQ charge-coupled device camera (Roper Scientific, Evry, France). Images were acquired as described by LeBlanc et al (LeBlanc et al, 2004). The signal was processed by correcting each fluorescence image for background fluorescence.…”

Angiotensin II-induced aortic ring constriction is mediated by phosphatidylinositol 3-kinase/L-type calcium channel signaling pathway

“…Consistent with this, our results showed that pharmacological inhibition of PI3K strongly attenuated AngII-induced calcium mobilization and VSMC contraction ( Figure 3A and 4A). PI3K-dependent activation of calcium mobilization was further demonstrated by Le Blanc et al (2004). They showed that PIP3, which is a product of PI3K, can directly activate L-type calcium channels.…”

“…Although PLC-β-dependent intracellular calcium mobilization during AngII stimulation is important for VSMC contractions, recent evidence also supports the idea that AngII increases myocardial activity through the augmentation of inward calcium currents through L-type calcium channels (Baker et al, 1992). Other evidence has supported the argument that G βγ directly activates PI3Kγ isoform to generate PIP 3 (Viard et al, 1999), which eventually stimulates L-type calcium channels in vascular myocytes from portal vein (Le Blanc et al, 2004). However, there is no direct evidence that PI3K-dependent calcium mobilization is important for vascular constriction upon AngII stimulation.…”

Calmodulin potentiates Gβγ activation of phospholipase C-β3

“…However, the PIP strip ® overlay assays did reveal a previously unappreciated affinity of PLCβ3 and PLCβ1 for PIP3. PIP3 is a membrane phospholipid that has a well-deserved reputation as a regulatory lipid in a variety of cell signaling pathways [41][42][43][44][45], including a reciprocal association with calmodulin [29,46] in other protein contexts. In addition to demonstrating an affinity of PLCβ3 and PLCβ1 for PIP3, the PIP strip ® overlay assay also revealed that PLCβ isozymes have different affinities for synthetic and wild-type lipids.…”