Ca channel pharmacology.

M.A. Tester mat10 at CUS.CAM.AC.UK
Tue Jul 5 13:41:13 EST 1994

Dear Neuroscience-netters,

Here is a second question from us plant-people, this time about
the pharmacology of (channel-mediated) Ca-45 fluxes in vesicles. There 
has not been that much work done on such measurements in plants,
but a couple of recent papers have appeared claiming to have done
this work (Marshall et al., 1994: Plant J. 5(5), 683-694; Huang et al., 1994:
PNAS 91, 3473-3477). The interesting (wierd?) thing is that both papers
report effective insensitivity of the Ca fluxes to verapamil. 

In contrast, our own work (Pineros & Tester, 1994: Planta, in press) 
with similar material shows high affinity inhibition by verapamil. The
difference is that in our work, we incorporate vesicles into planar lipid
bilayers and measure single Ca channels electrically.  (Interestingly,
measurements of Ca-45 fluxes into protoplasts prepared from two
other higher plant tissues also show sensitivity to low concentrations of
verapamil: Graziana et al., 1988: Biochemistry 27, 764-768; Rengel & Elliott,
1992: Plant Physiol. 98, 632-638).

Is there any precedence for Ca channels 'becoming' insensitive to
organic antagonists such as verapamil when the channel activity
is measured in vesicles? If so, is this commonly seen? And why is this


With many thanks - we look forward to any feedback on this.

Yours sincerely,

Mark Tester & Miguel Pineros

Department of Plant Sciences,

University of Cambridge,

Downing St,

Cambridge, CB2 3EA,

Tel. + 44 223 333918
Fax  + 44 223 333953

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