Guanine nucleotides mediate stimulatory and inhibitory effects on cerebral-cortical membrane phospholipase C activity.
In cerebral-cortical membranes, hydrolysis-resistant guanine nucleotides exert a dual regulatory effect on phospholipase C activity. Nanomolar concentrations of guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) or guanosine 5'-[gamma-thio]triphosphate (GTP[S]) inhibited basal phospholipase C activity, with a maximum inhibition of 30% at 10 nM. Increasing the concentration of p[NH]ppG or GTP[S] to over 10 nM resulted in a reversal of the inhibitory effect and onset of stimulation of phospholipase C activity. These inhibitory effects were blocked by 100 microM-guanosine 5'-[beta-thio]diphosphate. GTP was relatively ineffective in producing either stimulation or inhibition of phospholipase C activity. Similarly, ATP, adenosine 5'-[beta gamma-imido]triphosphate and GDP were also ineffective. Expression of the dual effects of guanine nucleotides was affected by the Mg2+ concentration. At 0.3 mM-Mg2+, both the inhibitory and the stimulatory components of p[NH]ppG action were evident. At 2.5 mM-Mg2+, only p[NH]ppG stimulation was observed. Pertussis-toxin treatment blocked the p[NH]ppG-mediated inhibition of phospholipase C activity. These results demonstrate that non-hydrolysable guanine nucleotides exert both a stimulatory and an inhibitory effect on membrane phospholipase C activity. These effects may be mediated through distinct GTP-binding proteins.
Litosch
I
I
Department of Pharmacology, University of Miami School of Medicine, FL 33101.
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D006150:Guanine Nucleotides / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013873:Thionucleotides / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D006150:Guanine Nucleotides; D013873:Thionucleotides; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D010738:Type C Phospholipases