Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Zona fasciculata/reticularis (ZFR) cells, isolated from the bovine adrenal cortex, secreted cortisol in response to acetylcholine (AcCh). The response was present in freshly isolated cells and in cells maintained in primary culture, reaching a maximum after 48-72 h and thereafter declining. Cells maintained in primary culture for 72 h secreted cortisol with an ED50 at 1.2 x 10(-6) M. The potent inhibition of AcCh-stimulated secretion by atropine, and the relative ineffectiveness of nicotine or nicotinic antagonists, were consistent with a predominantly muscarinic response to AcCh in these cells. A selective M1-receptor agonist, McN-A-343, had no effect on cortisol secretion whereas the M3 antagonist, hexahydro-sila-difenidol, produced a dose-dependent inhibition of AcCh-stimulated cortisol secretion. These findings are consistent with AcCh mediating its effects on cortisol secretion through an M3 receptor. While AcCh had no effect on cAMP formation, a dose-dependent increase in [3H]phosphoinositols (identified using high-performance liquid chromatography (HPLC)) occurred in a manner that was not dependent on an influx of extracellular Ca2+. Detailed HPLC analysis of the formation of 3H-labelled phosphoinositols and glycerophosphoinositols from pre-labelled cells over the period 0-15 min showed that the earliest significant rise was in Ins(1,4,5)P3 at 5 s, followed by later rises in InsP1, InsP2 and Ins(1,3,4)P3. Additional studies using cells loaded with fura-2 indicator revealed a 1.6-fold increase in [Ca2+]i from a mean resting value of 75 nM in response to 10(-4) M AcCh. Furthermore, the rise in Ca2+ was not abolished by lowering extracellular Ca2+ to resting cytosolic levels, suggesting the mobilisation of an intracellular pool. These observations indicate that AcCh promotes rapid activation of a Ca2(+)-independent and polyphosphoinositide-specific phospholipase C, and that the Ins(1,4,5)P3 formed releases Ca2+ from an intracellular pool. The stimulation by AcCh of this signal transduction mechanism is consistent with our conclusion, based on the effects of the selective muscarinic agonist and antagonist on cortisol secretion, that the AcCh receptor is of the M3 subtype. We conclude that AcCh, acting through an M3 receptor coupled to phospholipase C, regulates cortisol secretion at the cellular level in bovine adrenal ZFR cells.
 ...
PMID:Acetylcholine stimulates cortisol secretion through the M3 muscarinic receptor linked to a polyphosphoinositide-specific phospholipase C in bovine adrenal fasciculata/reticularis cells. 196 58

The effect of a variety of proteolytic, glycosidic and lipid hydrolyzing enzymes on the ability of mouse egg plasma membrane to interact with sperm was evaluated in this study. Zona-free mouse eggs were exposed to enzymes at various concentrations, washed, and inseminated; the number of sperm attached to or having penetrated the egg plasma membrane was determined at 20 and 180 min post-insemination, respectively. The proteases trypsin and chymotrypsin caused concentration-dependent reductions in both sperm attachment and sperm penetration levels when eggs were incubated at enzyme concentrations ranging from 1- to 1000 micrograms/ml for 30 min prior to insemination. Time-course studies revealed significant inhibition of both sperm attachment and sperm penetration levels after treating zona-free eggs for 5 min at 1000 micrograms/ml of either trypsin or chymotrypsin. Several of the phospholipases tested, including phospholipases C, D, and A2, had no inhibitory effect on sperm penetration levels, with phospholipase C and A2 (100 micrograms/ml) causing inhibition of sperm attachment. Of the glycosidic enzymes evaluated, glucuronidase (1000 micrograms/ml) caused significant inhibition of sperm binding but not sperm penetration, and glucosidase, galactosidase, and neuraminidase had no effect on either sperm attachment or sperm penetration. These findings indicate that the ability of the mouse egg plasma membrane to fuse with sperm can be preferentially altered by treatment with proteases.
 ...
PMID:Enzymatic alteration of the ability of mouse egg plasma membrane to interact with sperm. 306 84

The binding of the spermatozoon to the oocyte zona pellucida (ZP) occurs via specific receptors localized over the anterior head region of the spermatozoon. Zona pellucida binding stimulates the spermatozoa to undergo the acrosome reaction resulting in the release of hydrolytic enzymes and in the exposure of new membrane domains, both of which are essential for fertilization. We suggest that ZP binds to at least two different receptors in the plasma membrane. One (R) is a Gi-coupled receptor that activates phospholipase C (PLC) beta 1. The other (TK) is a tyrosine kinase receptor coupled to PLC gamma. Binding to R would regulate adenylyl cyclase (AC) leading to elevation of cAMP and protein kinase (PKA) activation. The PKA activates a voltage-dependent Ca2+ channel in the outer acrosomal membrane which releases Ca2+ from the interior of the acrosome to the cytosol. This is the first, relatively small, rise in [Ca2+]i (I) which leads to activation of the PLC gamma. The products of phosphatidyl-inositol bisphosphate (PIP2) hydrolysis by PLC diacylglycerol (DAG) and inositol-trisphosphate (IP3) will lead to PKC translocation to the plasma membrane and its activation. PKC opens a voltage-dependent Ca2+ channel (L) in the plasma membrane, leading to the second (II) higher increase in [Ca2+]i. The Gi or TK can also activate an Na+/H+ exchanger leading to alkalization of the cytosol. PKC also activates phospholipase A2 (PLA2) to generate arachidonic acid (AA) from membrane phospholipids. AA will be converted to prostaglandins (PG) and leukotriens (LT) by the enzymes cyclooxygenase (COX) and lipoxygenase (LOX) respectively. The increase in [Ca2+]i and pH leads to membrane fusion and acrosomal exocytosis.
 ...
PMID:The biochemistry of the acrosome reaction. 923 45

Prospective clinical studies informed by cloning and sequencing of sperm surface receptors and metal ion channels have elucidated critical early steps in the acrosome reaction that explain aspects of metal ion-related male infertility. Induction of the acrosome reaction is proposed to include non-nuclear progesterone receptor activation of Shaker-related sperm head voltage-gated potassium ion channels (VGKC). Men express VGKC isoforms with differing sensitivities to lead (Pb(2+)) inhibition, thus explaining interindividual variabilities in Pb(2+)-related male infertility. VGKC opening induces calcium (Ca(2+)) transients, and a signalling cascade induced by zona receptor aggregation requires an actin cytoskeleton created by the VGKC-induced Ca(2+) transients. Actin polymerization and stabilization, favoured by zinc (Zn(2+)) and depolymerized by cadmium (Cd(2+)), may mediate low Zn(2+) and high Cd(2+) infertile states. Zona receptor aggregation induces phosphotyrosine signals at sites, including sperm voltage-dependent Ca(2+) channels (VDCC), intermediate in electrophysiology between T- and L-type channels. Sperm surface VDCC localize at the sperm equatorial segment, the terminus of zona receptor translocation. Opening of VDCC admits a second Ca(2+) wave that activates phospholipase C phosphorylated in the zona receptor cascade. Phospholipase C induces fusogenic lipids and activates actin-severing proteins, depolymerizing the actin cytoskeleton and permitting apposition and fusion of acrosomal and plasma membranes.
 ...
PMID:Receptors and channels regulating acrosome reactions. 1184 26