MS: ***

I write on behalf of the Chairman to Inform you that your manuscript on "Title" has been carefully considered for publication in the Joumal . Your study is clearly of interest but for various reasons acceptance of your manuscript has been precluded.

You will see from the enclosed criticisms that a number of important problems have been identified. Having taken into account the weight of the objections raised and the amount of additional work that would be required to justify giving further editorial consideration to your manuscript, I do not believe that the difficulties can be satisfactorily resolved by simple revision. I regret to have to nform you that your manuscript has, therefore, not been accepted for publication.

Thank you, nevertheless, for having let us see your work.

Yours sincerely.

Referee's Report to Authors

The main point that the paper makes is that rat megakaryocytes have thrombin receptors. This is a novel observation but given the fact that the megakaryocyte is the progenitor of platelets, it is hardly surprising. The associated observations of (presumed) repetitive calcium transients and effects of trypsin are also not particularly novel for cells which have thrombin receptors (1) . The potentially novel aspects have not been investigated very thoroughly. For example, the possibility that the megakarocyte receptor differs from the platelet receptor is a possibility which deserves further study. The effect of the thrombin receptor agonist peptide (s) on megakaryocytes have not been studied which is a curious omission from a paper on the pharmacological characterisation of the thrombin receptor.

The following are detailed points which would need to be addressed for the manuscript to be suitable for publication:

-Parts A and B in Figure 1 are the wrong way around compared to the legend.

-In Figure IA (as shown), what is labelled as frequency is the interval. It should be made clearer over what period the frequency was measured as it clearly reduced during the washout period.

-Some parts of the text suggest that thrombin is not a serine protease e.g. p9, para l, sentence 6 should be changed to "The IKCa oscillation was also " Also, describinginduced by the application of another serine protease. chymotrypsin as "another type of protease" (p9, para l, sentences 11 & 12) suggests that it isn't a serine protease which is incorrect.

-Demonstrating cross-desensitisation is suggestive but does not necessarily prove that the same receptor is involved in signalling thrombin and trypsin. It could just be an example of heterologous desensitisation between distinct receptors (2) .

-References to IP3 should specify that it is D-Insl,4,5P3 . It should be made clear what species the thrombin, trypsin etc used was derived from and whether proteins such as hirudin or aprotinin etc were natural or recombinant .

1.Jones et al (1989) Mol.Pharmacol.36,142-149.

2.Selak,M (1994) Biochem J.297,269-275.

Editor's Report to Authors

The authors have conducted some Interestlng studies with quite a sophisticated approach. It is therefore surprising that they have not studied the effect of the thrombin receptor agonist peptides on these cells .

Whilst they have demonstrated cross-desensitisation this does not prove that the same receptor is involved.

The discussion is speculative in parts. There has also been published recently studies by Plantier et al (Br. J. Haematol 87:755-762 1994) that demonstrate that thrombin, via the thrombin receptor, inhibits megakaryocyte progenitor growth. the authors may wish to modify some of their ideas as a result.

There is an error in the references on P19.

Better quality figures would be required for publication.