@article {Sato497, author = {K Sato and M Hori and H Ozaki and H Takano-Ohmuro and T Tsuchiya and H Sugi and H Karaki}, title = {Myosin phosphorylation-independent contraction induced by phorbol ester in vascular smooth muscle.}, volume = {261}, number = {2}, pages = {497--505}, year = {1992}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {In isolated rat aorta, carotid artery, tail artery, rabbit aorta and mesenteric artery, but not in ear artery, 1 microM 12-deoxyphorbol 13-isobutyrate (DPB) induced a sustained contraction. However, DPB increased cytosolic Ca++ concentration ([Ca++]i) only in rat aorta and carotid artery. Similar results were obtained with phorbol 12,13-dibutyrate, although the inactive phorbol ester, 4-alpha-phorbol 12,13-dibutyrate, was ineffective. In rat aorta, DPB-induced contraction was followed by an increase in 20 kDa myosin light chain (MLC) phosphorylation. Both contraction and MLC phosphorylation stimulated by DPB were greater than those due to high K+ for a given increase in [Ca++]i. A Ca++ channel blocker, verapamil, decreased the DPB-induced increments in [Ca++]i and MLC phosphorylation to their respective resting levels, although contraction was inhibited only slightly. In the absence of external Ca++ (with 0.5 mM ethyleneglycol bis(beta-aminoethyl-ether)tetraacetic acid), DPB induced sustained contraction without increasing [Ca++]i or MLC phosphorylation. This contraction was followed by an increase in stiffness and force recovery after a shortening step. These results suggest that the contraction induced by DPB in rat aorta is due to increase in [Ca++]i followed by MLC phosphorylation and Ca++ sensitization of MLC phosphorylation. In the presence of verapamil or in the absence of external Ca++, DPB may increase cross-bridge cycling by activating an unknown mechanism that is not dependent on an increase in MLC phosphorylation.}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/261/2/497}, eprint = {https://jpet.aspetjournals.org/content/261/2/497.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }