Phorbol 12,13-dibutyrate, an activator of protein kinase C, stimulates both contraction and Ca2+ fluxes in dog saphenous vein.
The vascular effects of phorbol 12,13-dibutyrate (PDBu) were studied in the dog saphenous vein. PDBu (1 microM) caused contraction (0.58 +/- 0.22 g/mg wet wt.) and Ca uptake (74.2 +/- 41.2 mumol/kg wet wt.) which were unaffected by 10 microM phentolamine (N = 6). The PDBu-induced contraction was greatly (60-80%) inhibited in Ca2+-free solution. 45Ca efflux measurements performed in Ca2+-free solution showed that PDBu did not cause Ca release from intracellular storage sites. The contractile response to PDBu (1 nM-1 microM) was significantly correlated with the magnitude of Ca uptake; contraction and the rise in tissue Ca2+ also had a similar time course. Correlation between the two measures persisted when the responses to PDBu were augmented by co-administration with 20 mM KCl. However, no synergism occurred between the two agonists. Both the contraction and Ca uptake responses to PDBu were reduced by nifedipine and verapamil, each at 1 microM. In the Triton X-100 skinned saphenous vein, where the voltage-dependent Ca channel is not functional, 10 microM PDBu did not cause contractions in the presence of 0.1 microM Ca2+. Thus, contraction of the intact saphenous vein by PDBu characteristically exhibits great Ca dependence and PDBu seems to activate the voltage-dependent Ca channel, presumably through stimulation of protein kinase C; the ensuing Ca entry is primarily responsible for contraction. However, the mechanism responsible for the PDBu-induced contractions that are resistant to Ca2+-free PSS or Ca entry blockers remains to be defined.(ABSTRACT TRUNCATED AT 250 WORDS)
Chiu
P J
PJ
Department of Pharmacology, Schering-Plough Corporation, Bloomfield, New Jersey 07003.
Tetzloff
G
G
Chatterjee
M
M
Sybertz
E J
EJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D012501:Saphenous Vein / Q000187:drug effects
D010656:Phenylephrine; D015240:Phorbol 12,13-Dibutyrate; D011189:Potassium Chloride; D011493:Protein Kinase C; D009543:Nifedipine; D002118:Calcium