Platelet-activating factor (PAF) induces contraction of saponin-skinned smooth muscle of coronary artery.

The effect of platelet-activating factor (PAF) on the development of isometric tension by saponin-skinned coronary artery was studied. PAF caused two types of contractions of coronary smooth muscle cells (SMC): (i) rapid, transient (phasic) contractions of SMC were induced by inositol 1,4,5-trisphosphate dependent Ca2+ release from sarcoplasmic reticulum (SR); (ii) slow sustained (tonic) contractions were induced by increase in Ca(2+)-sensitivity of the contractile apparatus of SMC by protein kinase C activation. The present results support the hypothesis that, in SMC of coronary artery, PAF receptors are located not only on the plasma membrane, but also on the SR membranes.