Stroke/Cerebral Vasospasm

Re: Mitogen-activated kinase

John Zhang

On Tue Dec 8, R Loch Macdonald wrote
>I was interested to read your work on MAPK and contraction.  We have begun similar experiments using pure hemoglobin as the contractant.  I note that you observed effects at 30 uM and above.  The question arises as to whether you have carried out control measurements of the concentration of PD98? required to inhibit contraction to an agonist that is known to act via MAPK eg. thrombin and that that concentration does not affect contraction to eg. KCl.  Second, what compound in the hemolysate does this?  We previously found some of the effect of acute hemolysate is due to ATP but why, for example, would hemoglobin do this?  IS it a direct or indirect effect?

You have raised an important point. I am not sure that we had done PH98059 with KCl. I agree that we should do it. But the question is KCL-induced contration is also regulated by tyrosine kinases and MAPK is a substrate of tyrosine kinases. Thus, PD98059 may reduce the contraction to KCl as well. Similarly, KIm's paper in JNS in the summer demonstrated similar results that genistein and tyrphostin reduced the contraction to KCL. Several patch-clamp studies showe that genistein and tyrphostin directly inhibit L-type calcium channels in different tissues. since we believe there are cross-links between G-protein coupled and growth factor receptors as well as KCl-induced contraction, find a positive or negitive control may prove to be difficult. Most g-protein receptors activate tyrosine kinases and MAPK. Tyrosine kinases can be activated by both PKC and calcium. Second, hemolysate is a complex that contains many agonists and may be most of them have an effect on tyrosine or MAP kinases. ATP certainly has since some has regard ATP as a "growth factor." using pure hemoglobin may answer your question. We are doing the breakdowns using hemin and bilirubin.
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