Protein kinase C plays no role in KCl-induced vascular contraction in Ca(2+)-free medium.
OBJECTIVE
To examine the role of protein kinase C (PKC) on the sustained contractile responses of rat aorta to high KCl in isotonic Ca(2+)- and Mg(2+)-free solutions.


METHODS
The effects of phorbol 12-myristate 13-acetate (PMA, a PKC activator) and Calphostin C (a selective PKC inhibitor) were observed on the sustained contraction of rat aorta induced by K+ 136 mmol.L-1. EGTA (100 mumol.L-1) was added to prepare the Ca(2+)-free medium and EDTA (100 mumol.L-1) was added to reduce or remove the Mg2+.


RESULTS
Aortic contraction to KCl was prominent in low Mg2+ medium and was enhanced by EDTA (K-EDTA contraction). Such contraction was concentration-dependently inhibited by Mg2+, but was not affected by Calphostin C 1 mumol.L-1. Pretreatment of the aortic preparations with PMA (0.8 mumol.L-1) potentiated the contraction to KCl in Ca(2+)-free, low Mg2+ medium and higher concentration of Mg2+ was required to cause relaxation. Such a reduced sensitivity to Mg2+ in the presence of PMA was partially reversed by Calphostin C and was accompanied by an increased sensitivity to Ca2+, which concentration-dependently caused contraction following Mg(2+)-induced relaxation. However, in the presence of EDTA 100 mumol.L-1 (eg, Mg(2+)-free medium), the maximal contraction to KCl in Ca(2+)-free medium was not affected by PMA or Calphostin C.


CONCLUSIONS
KCl-induced contraction in Ca(2+)-free and Mg(2+)-free + EDTA 100 mmol.L-1 medium was not affected by PMA or Calphostoin C, indicating that PKC plays no role in such contractile responses.
Kwan
C Y
CY
Department of Physiology, Faculty of Medicine, University of Hong Kong, Hong Kong.
Kravtsov
G M
GM
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009281:Naphthalenes / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D009281:Naphthalenes; D011189:Potassium Chloride; D011493:Protein Kinase C; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium