Purification, G Protein Activation, and Partial Amino Acid Sequence of a Novel Phospholipase C from Squid Photoreceptors†

Biochemistry ◽  
1998 ◽  
Vol 37 (25) ◽  
pp. 9064-9072 ◽  
Author(s):  
Jane Mitchell ◽  
Linnia H. Mayeenuddin
Keyword(s):  
Amino Acid ◽  
Amino Acid Sequence ◽  
Phospholipase C ◽  
G Protein ◽  
Partial Amino Acid Sequence ◽  
Protein Activation ◽  
G Protein Activation

Myogenic tone is coupled to phospholipase C and G protein activation in small cerebral arteries

1993 ◽  
Vol 265 (1) ◽  
pp. H415-H420 ◽  
Author(s):  
G. Osol ◽  
I. Laher ◽  
M. Kelley
Keyword(s):  
Phospholipase C ◽  
G Protein ◽  
G Proteins ◽  
Inhibitory Concentration ◽  
Cerebral Arteries ◽  
Myogenic Tone ◽  
Potassium Depolarization ◽  
Protein Activation ◽  
G Protein Activation ◽  
Transduction Mechanisms

The cellular transduction mechanisms underlying the response of blood vessels to mechanical forces such as pressure or stretch are largely unknown. In this report we test the hypothesis that myogenic tone in the cerebral circulation is coupled to activation of phospholipase C (PLC) and G proteins. Rat posterior cerebral arteries (luminal diam 189 +/- 4 microns) were cannulated in an arteriograph and allowed to develop myogenic tone at 75 mmHg (122 +/- 6 microns; P < 0.01). Exposure to U-73122, an inhibitor of PLC, produced concentration-dependent vasodilation, with near-maximal (> 90%) inhibition at concentrations > 3 microM (50% inhibitory concentration = 0.8 +/- 0.04 microM). The action of U-73122 was confirmed by demonstrating that constrictor responses to serotonin (PLC mediated) could be significantly attenuated or abolished at concentrations (0.5–1 microM) that were ineffective in antagonizing potassium depolarization or indolactam-induced constrictions (both PLC independent). Incubation in pertussis toxin (100 ng/ml, 2–2.5 h), an inhibitor of some G protein subtypes, reduced myogenic tone by 74 +/- 12%, with luminal diameters increasing from 129 +/- 7 to 160 +/- 7 microns. Conversely, nonspecific G protein activation using AlF-4 (NaF+AlCl3, 0.5-5 mM) significantly increased myogenic tone by 86 +/- 9%, reducing luminal diameters from 132 +/- 6 to 88 +/- 8 microns (P < 0.01). Together, these findings suggest that 1) PLC is activated in arteries that possess myogenic tone, 2) pharmacological inhibition of PLC results in a virtual loss of pressure-induced constriction, and 3) G proteins may modulate mechanotransduction through pathways superimposed on basal myogenic tone.

scholarly journals Identification of Gα11 as the phospholipase C-activating G-protein of turkey erythrocytes

1993 ◽  
Vol 290 (3) ◽  
pp. 765-770 ◽  
Author(s):  
D H Maurice ◽  
G L Waldo ◽  
A J Morris ◽  
R A Nicholas ◽  
T K Harden
Keyword(s):  
Amino Acid ◽  
Amino Acid Sequence ◽  
Phospholipase C ◽  
G Protein ◽  
Expression System ◽  
Cdna Libraries ◽  
Dependent Manner ◽  
Alpha Subunits ◽  
G Protein Alpha Subunit ◽  
G Alpha Q

A 43 kDa phospholipase C-activating protein has been purified previously from turkey erythrocytes and shown to express immunological properties expected of that of the Gq family of G-protein alpha-subunits [Waldo, Boyer, Morris and Harden (1991) J. Biol. Chem. 266, 14217-14225]. Internal amino acid sequence has now been obtained from this protein which shares 50-100% sequence identity with sequences encoded by mammalian G alpha 11 and G alpha q cDNAs. To identify the purified protein unambiguously, it was necessary to compare its amino acid sequence with the sequence encoded by avian G-protein alpha-subunit cDNA. As such, mouse G alpha q was used as a probe to screen turkey brain and fetal-turkey blood cDNA libraries. A full-length cDNA was identified that encodes avian G alpha 11, on the basis of its 96-98% amino acid identity with mammalian G alpha 11. All eight peptides sequenced from the turkey erythrocyte phospholipase C-activating protein are completely contained within the deduced amino acid sequence of the avian G alpha 11 cDNA. Expression of this cDNA in Sf9 cells by using a baculovirus expression system resulted in the production of a 43 kDa protein that reacts strongly with antisera to the Gq family of G-protein alpha-subunits and activated purified avian phospholipase C in an AlF4(-)-dependent manner. Taken together, these results unambiguously identify the protein purified from turkey erythrocytes, on the basis of its capacity to activate avian phospholipase C, as G alpha 11.

Opioid-Activated Postsynaptic, Inward Rectifying Potassium Currents in Whole Cell Recordings in Substantia Gelatinosa Neurons

1998 ◽  
Vol 80 (6) ◽  
pp. 2954-2962 ◽  
Author(s):  
S. P. Schneider ◽  
W. A. Eckert ◽  
A. R. Light
Keyword(s):  
Membrane Potential ◽  
G Protein ◽  
Potassium Currents ◽  
Substantia Gelatinosa ◽  
Opioid Agonist ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Protein Activation ◽  
G Protein Activation ◽  
Whole Cell Recordings

Schneider, S. P., W. A. Eckert III, and A. R. Light. Opioid-activated postsynaptic, inward rectifying potassium currents in whole cell recordings in substantia gelatinosa neurons. J. Neurophysiol. 80: 2954–2962, 1998. Using tight-seal, whole cell recordings from isolated transverse slices of hamster and rat spinal cord, we investigated the effects of the μ-opioid agonist (d-Ala2, N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO) on the membrane potential and conductance of substantia gelatinosa (SG) neurons. We observed that bath application of 1–5 μM DAMGO caused a robust and repeatable hyperpolarization in membrane potential ( V m) and decrease in neuronal input resistance ( R N) in 60% (27/45) of hamster neurons and 39% (9/23) of rat neurons, but significantly only when ATP (2 mM) and guanosine 5′-triphosphate (GTP; 100 μM) were included in the patch pipette internal solution. An ED50 of 50 nM was observed for the hyperpolarization in rat SG neurons. Because G-protein mediation of opioid effects has been shown in other systems, we tested if the nucleotide requirement for opioid hyperpolarization in SG neurons was due to G-protein activation. GTP was replaced with the nonhydrolyzable GTP analogue guanosine-5′- O-(3-thiotriphosphate) (GTP-γ-S; 100 μM), which enabled DAMGO to activate a nonreversible membrane hyperpolarization. Further, intracellular application of guanosine-5′- O-(2-thiodiphosphate) (GDP-β-S; 500 μM), which blocks G-protein activation, abolished the effects of DAMGO. We conclude that spinal SG neurons are particularly susceptible to dialysis of GTP by whole cell recording techniques. Moreover, the depletion of GTP leads to the inactivation of G-proteins that mediate μ-opioid activation of an inward-rectifying, potassium conductance in these neurons. These results explain the discrepancy between the opioid-activated hyperpolarization in SG neurons observed in previous sharp electrode experiments and the more recent failures to observe these effects with whole cell patch techniques.

Sign in / Sign up

Export Citation Format

Share Document