Flash photolysis of intracellular caged GTP gamma S increases L-type Ca2+ currents in cardiac myocytes.
L-type calcium currents were recorded from isolated ventricular myocytes using standard patch-clamp methods. Rapid release of photolabile guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), tetralithium salt, by flash photolysis of intracellular caged-GTP gamma S increased the magnitude of the L-type calcium current: an effect independent of the ultraviolet flash per se or the production of photolytic by-products. This increase in calcium current was markedly reduced by intracellularly applied guanosine 5-O-(thiodiphosphate), trilithium salt or by an excess of GTP gamma S. It is therefore likely that rapid release of GTP gamma S intracellularly in the absence of an agonist can, via a G protein-mediated mechanism, cause L-type calcium current activation. In the presence of Rp-adenosine 3,5-mono-thionophosphate (Rp-cAMP), photoreleased GTP gamma S results in a transient and much reduced increase in the amplitude of the L-type calcium current. We conclude that activation of Gs coupled to adenylate cyclase and ultimately cAMP-dependent phosphorylation may be primarily responsible for L-type channel activation, although a fast membrane-delimited (direct) pathway, not involving cytoplasmic second messengers, may also contribute to this effect.
Kozlowski
R Z
RZ
University Laboratory of Physiology, Oxford, United Kingdom.
Twist
V W
VW
Brown
A M
AM
Powell
T
T
D000818:Animals; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004229:Dithiothreitol / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005978:Glutathione / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology* / Q000031:analogs & derivatives; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000528:radiation effects; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles; D066298:In Vitro Techniques; D007700:Kinetics; D010782:Photolysis; D013873:Thionucleotides / Q000494:pharmacology* / Q000528:radiation effects
C057003:1-(2-nitro)phenylethyl-P(3)-guanosine 5'-O-(3-thio)triphosphate; D015220:Calcium Channels; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D005978:Glutathione; D002118:Calcium; D004229:Dithiothreitol