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Progesterone metabolites enhance GABA activities
TPS - September 19007iVol.81
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usedtu&&qxet
th? rde ufPKC’
Proteinkinase C inhibitorsare not We read with interest the article by Hidaka and Hagiwara on the pharmacology of protein kinase C (PKC) inhibitors (TipS, May 1987, pp. 162-X4) and share their view that many, if not all of the compounds that are described as PKC inhibitors However, we wish to express our reservation about their classification of the isoquinoline sulphonamide ‘H-7‘ as a spedfie inhibitor of PKC. This classification seems to defy the logic af their own observationsl. H-7 inhibits three different protein kinases with equal activity, having Ki vahres of S-6 n&r for cyclic nucleotide (CAMP and cGMP)-dependent kinases as well
as for PKC, but it is less active as an inhibitor of myosin light chain kinase (& = 97 @M). It is competitive for the ATP site of the kinases and there is no evidence from isolated enzyme studies that H-7 interacts with the diacyiglycerol site or shows any other form of selectivity for PKC. Thus, H-7 should not be described as a specific inhibitor of PKC, although it may have this effeet under experimental conditions when the activity of cyclic nucleotide-dependent protein kinases is low, Hidaka and Hagiwara describe numerous experiments where H-7 inhibited various cellular responses stimulated by PKC-activat-
activities recerrt TPS review by Lambe& Peters and Cottrel~~gave an excellent description of the work done over the last few years in studying the intriguing interaction between certain steroids and the GABAA receptor. i should like to add a brief description of more recent work that has appeared in print since the review of Lambert ef af. was written. The authors describe the stereoselectivity for steroid action in enhancing GABA, activity being restricted to compounds with a saturated A ring and a hydroxyl group at C3 in the or-configuration; an extensive stru&rri+activity study2 confirms these requirements and indicates also the necessity of the ketone group at C20. The ability of steroids to enhance ~Sp~~Sff~ to pharmacologically applied GABA also extends-to the GARA-mediated inhibitory postsynaptic current (IPSC) at inhibitory synapses between cul-
The
@ 1987, Elsevier Pubkationr.
Cambridge
0165 - 6147/67~.~
tured rat hippocampal neurons. Both the steroid anaesthetic alfaxalone3 and two hormonal metabolites” prolong the IPSC decay time, by a factor of up to lo-fold, Finally, therelevanceof thein-vitro workon the GABA receptors of cultured neurones2*3 and chrcmaffin ceii&” is demonstrated by the in-viva experiments of Smith and eoworkerss. In rat cerebellar Purkinje cells it was found that the ability of GABA to decrease neuronal firing rate was augmented within 2-5 min. of progesterone injection or local application. It was subsequently shown that one of the metabolites identified in the in-vitm studies also enhanced the inhibitory action of GABA on Purkinje cell firing rate, in a rapid and potent mann&. Since progesterone is inactive in the in+itru experiments, these results can be explained if the hormone were metabolized locally to active metaboliteis). This find-
ing phorbol esters. These observations are consistent with H-7 being an inhibitor of PKC. However, even this interpretation may sometimes be an oversimplification in view of the interactions between PKC and the cyclic nucleotide pathways in certain types of cell, e.g. inhibition of CAMP phosphodiesterase in hepatocytes’ and s~rn~a~o~ of guanylate cy&ise in human lymphocytes3. Therefore, we wish to emphasize that since H-7 is not a selective inhibitor of PKC this compound should not be used to interpret the role of PKC in complex cellular events that may also involve cyclic nucleotidedependent protein kinases. L. G. GARLAND, R. W. BON5EK AND BY.T. THOMPSON The Wel&xurreResearch Laborufories, I,nngley
Court, Beckenkan~,Kent BR? 33.9, UK.
References 1 Hidaka, II., Inagaki, M., Kawamoto, S. and Sasaki, Y. (1984) Biochemistry 23, SO36-5041 2 Irvine, F,, Pyne, N. J. and HousIay, M. D. (1986) FE&SLeft. 208,455-459 3 Coffey, R, G. (1986) Int, J. Biochem. l&3, 665-670
ing is very exciting since it indicates the formation from progesterone of potent neuroactive steroids in an intact living animal. It appears that earlier speculation of the possible physiological importailce of steroid&ABA interactions7,s may not be misplaced. NElL L. HARRTSON
References 1 Lamb&
J. J.. Peters, J. A. and Cotb-efl (1987) Trerzds Pkarm~~ol. Sei. 8, 224-227 Harrison, N. L., Majowska, M. D., Iiarrington, J. W. and Barker, J. L. (1987) J. Pknrmacol. Exp. Tker. 241,346-353 Harrison, N. L., Wcini, S. and Barker, J. L. (1987) J. Neurosci. 7,604-609 CottreIl, C. A., Lambert, J. J. and Paters, J. A. (1987) Br. 1. Pharmacof. 90,4915013 Smith, S. S., Waterhouse, 8, D., Chapin, J. K. and Woodward, D.J. (1987) Brain G. A.
2 3 4 5
Res. 4M3,353-559
6 Smith, S. S., Waterhouse, 8. D. and Woodward, D. J. (1987) Bruin Res. Bull. l&739-747
7 111.A.” u,..+o” .LI I% L. and Slmmonds: M. A. ’ (19%) Brain Res. 323,287-292 8 Majswska, M.D., HarrIson, N. L. Schwartz, R. D., Barker, J. L. and Paw], S. M. (1986) Science 232,1004-1007
‘~-~~u~d~ut~
usedtu&&qxet
th? rde ufPKC’
Proteinkinase C inhibitorsare not We read with interest the article by Hidaka and Hagiwara on the pharmacology of protein kinase C (PKC) inhibitors (TipS, May 1987, pp. 162-X4) and share their view that many, if not all of the compounds that are described as PKC inhibitors However, we wish to express our reservation about their classification of the isoquinoline sulphonamide ‘H-7‘ as a spedfie inhibitor of PKC. This classification seems to defy the logic af their own observationsl. H-7 inhibits three different protein kinases with equal activity, having Ki vahres of S-6 n&r for cyclic nucleotide (CAMP and cGMP)-dependent kinases as well
as for PKC, but it is less active as an inhibitor of myosin light chain kinase (& = 97 @M). It is competitive for the ATP site of the kinases and there is no evidence from isolated enzyme studies that H-7 interacts with the diacyiglycerol site or shows any other form of selectivity for PKC. Thus, H-7 should not be described as a specific inhibitor of PKC, although it may have this effeet under experimental conditions when the activity of cyclic nucleotide-dependent protein kinases is low, Hidaka and Hagiwara describe numerous experiments where H-7 inhibited various cellular responses stimulated by PKC-activat-
activities recerrt TPS review by Lambe& Peters and Cottrel~~gave an excellent description of the work done over the last few years in studying the intriguing interaction between certain steroids and the GABAA receptor. i should like to add a brief description of more recent work that has appeared in print since the review of Lambert ef af. was written. The authors describe the stereoselectivity for steroid action in enhancing GABA, activity being restricted to compounds with a saturated A ring and a hydroxyl group at C3 in the or-configuration; an extensive stru&rri+activity study2 confirms these requirements and indicates also the necessity of the ketone group at C20. The ability of steroids to enhance ~Sp~~Sff~ to pharmacologically applied GABA also extends-to the GARA-mediated inhibitory postsynaptic current (IPSC) at inhibitory synapses between cul-
The
@ 1987, Elsevier Pubkationr.
Cambridge
0165 - 6147/67~.~
tured rat hippocampal neurons. Both the steroid anaesthetic alfaxalone3 and two hormonal metabolites” prolong the IPSC decay time, by a factor of up to lo-fold, Finally, therelevanceof thein-vitro workon the GABA receptors of cultured neurones2*3 and chrcmaffin ceii&” is demonstrated by the in-viva experiments of Smith and eoworkerss. In rat cerebellar Purkinje cells it was found that the ability of GABA to decrease neuronal firing rate was augmented within 2-5 min. of progesterone injection or local application. It was subsequently shown that one of the metabolites identified in the in-vitm studies also enhanced the inhibitory action of GABA on Purkinje cell firing rate, in a rapid and potent mann&. Since progesterone is inactive in the in+itru experiments, these results can be explained if the hormone were metabolized locally to active metaboliteis). This find-
ing phorbol esters. These observations are consistent with H-7 being an inhibitor of PKC. However, even this interpretation may sometimes be an oversimplification in view of the interactions between PKC and the cyclic nucleotide pathways in certain types of cell, e.g. inhibition of CAMP phosphodiesterase in hepatocytes’ and s~rn~a~o~ of guanylate cy&ise in human lymphocytes3. Therefore, we wish to emphasize that since H-7 is not a selective inhibitor of PKC this compound should not be used to interpret the role of PKC in complex cellular events that may also involve cyclic nucleotidedependent protein kinases. L. G. GARLAND, R. W. BON5EK AND BY.T. THOMPSON The Wel&xurreResearch Laborufories, I,nngley
Court, Beckenkan~,Kent BR? 33.9, UK.
References 1 Hidaka, II., Inagaki, M., Kawamoto, S. and Sasaki, Y. (1984) Biochemistry 23, SO36-5041 2 Irvine, F,, Pyne, N. J. and HousIay, M. D. (1986) FE&SLeft. 208,455-459 3 Coffey, R, G. (1986) Int, J. Biochem. l&3, 665-670
ing is very exciting since it indicates the formation from progesterone of potent neuroactive steroids in an intact living animal. It appears that earlier speculation of the possible physiological importailce of steroid&ABA interactions7,s may not be misplaced. NElL L. HARRTSON
References 1 Lamb&
J. J.. Peters, J. A. and Cotb-efl (1987) Trerzds Pkarm~~ol. Sei. 8, 224-227 Harrison, N. L., Majowska, M. D., Iiarrington, J. W. and Barker, J. L. (1987) J. Pknrmacol. Exp. Tker. 241,346-353 Harrison, N. L., Wcini, S. and Barker, J. L. (1987) J. Neurosci. 7,604-609 CottreIl, C. A., Lambert, J. J. and Paters, J. A. (1987) Br. 1. Pharmacof. 90,4915013 Smith, S. S., Waterhouse, 8, D., Chapin, J. K. and Woodward, D.J. (1987) Brain G. A.
2 3 4 5
Res. 4M3,353-559
6 Smith, S. S., Waterhouse, 8. D. and Woodward, D. J. (1987) Bruin Res. Bull. l&739-747
7 111.A.” u,..+o” .LI I% L. and Slmmonds: M. A. ’ (19%) Brain Res. 323,287-292 8 Majswska, M.D., HarrIson, N. L. Schwartz, R. D., Barker, J. L. and Paw], S. M. (1986) Science 232,1004-1007