Abstract
The characteristics of the Ca2+ entry pathways that are activated by protein kinase C (PKC) in canine splenic artery were investigated. Phorbol 12, 13-dibutyrate (PDB) contracted tissues and increased Ca2+ influx. PDB-induced contraction was reduced by preincubation of tissues in Ca2+-free Krebs’ solution (1 mM EGTA) but was unaffected when Ca2+-free solution was applied after contraction was initiated with PDB. In contrast,45Ca influx and contraction induced by PDB were resistant to nifedipine, Cd2+, Gd3+, La3+, or Ni2+ whether added before or during exposure to PDB. Indeed, Cd2+ reduced45Ca2+ efflux and potentiated Ca2+influx, but not PDB-induced contraction. Norepinephrine (NE)-induced contractions were inhibited by preincubation in Ca2+-free Krebs’ solution (1 mM EGTA). Nifedipine (10 μM) led to a small reduction in the NE-induced contraction but was without effect on45Ca2+ influx. Pretreatment for 16 min with Cd2+, Gd3+, or La3+ (each 1 mM) reduced or abolished NE-induced contraction and Ca2+influx. Application of these cations after exposure to NE did not affect 45Ca2+ influx but reduced tension. The Q10 for the increase in 45Ca2+influx was approximately 2 for high K+ and NE, but 4 for PDB. The results suggest that stimulation of PKC in dog splenic artery activates a Ca2+ entry pathway that is resistant to di- and trivalent cations. The inhibition of Ca2+ influx by preincubating with cations during short-term exposure to NE may represent an action on Ca2+ turnover that precedes activation of PKC.
Footnotes
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Send reprint requests to: Dr. D. P. Westfall, Department of Pharmacology, School of Medicine, University of Nevada, Reno, NV 89557-0001. E-mail: westfall{at}admin.unr.edu
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↵1 This work was supported by National Institutes of Health Grant HL38126 (D.P.W.) and HL 40399 (K.D.K.).
- Abbreviations:
- PDB
- phorbol 12,13-dibutyrate
- PKC
- protein kinase C
- NE
- norepinephrine
- 4αPDD
- 4α-phorbol 12,13-didecanoate
- Received February 5, 1999.
- Accepted July 15, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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