Editorial report

The authors have attempted to define the role and regulation of intracellular Ca ATPases in determining the oscillations of intracellular Ca in megakaryocytes. They have used agents affecting the activity of various protein kinases and interpret the actions of these agents as directly affecting Ca-ATPase, rather than considering other targets.

Major points

l. The work relies heavily not only on the specificity of the various inhibitors used but also on the assumption that the only relevant target (in terms of Ca regulation) is the Ca-ATPase. It is highly unlikely that there are not other effects (e.g. generation of Ins P3, effects on Ins P3 receptors, Ca-channels in the plasma membrane, IKC~ also involved. In particular, it is extremely unwise to make any definite conclusions from experiments such as those in Fig. 3, where the combined effects of up to three different agents is observed. The observations may be interpretable in the way suggested by the authors, but there is really no means of knowing this.

2. p.8. It is highly unlikely that effects due to the plasma membrane Ca-ATPase can be ruled out. In most cell types, elevation of Cai causes increased Ca-ejection, and indeed the observation on p.8 1.3. means exactly this. Why else would stimulation in Ca-free medium cause a run down in the response? Also (p9) there is no evidence for CAM effects on SERCA type ATPases. Only plasma membrane type Ca-ATPases have the C-terminal extension which is the CAM-interacting domain.

3. The control ATP-evoked IKCa Oscillations shown at the start of the traces seem to vary markedly and to show a run-down phenomenon. This makes it difficult to tell whether PMA (Fig. 2) has done anyihing to the run-down which would not have happened anyway.

4. p.6. The authors state that the effects of CPA (Fig. Ia) and staurosparine (Fig. Ib) are the same. In fact, the shape of the signal shown is very different, being flat-topped for staurosparine and just showing a slower down-sweep for CPA.