Effects of phorbol 12,13-dibutyrate on the vascular tone and on norepinephrine- and potassium-induced contractions of cat cerebral arteries.
Phorbol 12,13-dibutyrate (PDB), an activator of protein kinase C (PKC), induced slow-developing sustained contractions in segments of cat middle cerebral arteries. PDB-induced responses were not affected by phentolamine (1 microM) and endothelium removal, and were reduced by 1-(5-isoquinoline sulfonyl)-2-methylpiperazine (25 microM) and staurosporine (10 nM), PKC inhibitors. Forskolin (25 microM) produced a rapid and marked vasodilation in segments contracted with PDB. The 4 alpha-phorbol 12,13-didecanoate, an inactive compound, induced slight vasodilation. Preincubation with nifedipine diminished the responses elicited by PDB at all concentrations used. Ca-free medium containing 3 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), but not 1 mM, markedly reduced the phorbol-induced responses at concentrations up to 10 nM. Nifedipine (0.1 microM) and forskolin (25 microM) produced a rapid and marked relaxation of PDB (10 nM)-evoked contractions in segments incubated in a Ca-free solution (1 mM EGTA), but PBD responses in 3 mM EGTA were not affected by nifedipine. PDB (10 and 100 nM) practically did not modify K-induced contractions, but reduced vasoconstrictions elicited by different norepinephrine concentrations; this effect was phorbol concentration and preincubation time-dependent. These results indicate that: 1) PDB induced PKC activation and contraction mainly produced by Ca entry (essentially at low PDB concentrations) through dihydropyridine-sensitive Ca channels; 2) the activated PKC has elevated sensitivity for Ca; 3) PKC may be involved in the alpha adrenoceptors desensitization, but did not play an important role in the norepinephrine-induced contraction in these arteries.
Departamento de Farmacologia y Terapéutica, Facultad de Medicina, Universidad Autónoma, Madrid, Spain.
M
M
Salaices
G
G
Balfagon
S
S
Arribas
M R
MR
de Sagarra
J
J
Marín
D000818:Animals; D002118:Calcium / Q000502:physiology; D002415:Cats; D002536:Cerebral Arteries / Q000187:drug effects* / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects*
D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine