SELECTIVE DISRUPTION BY PROTEIN KINASES OF G-protein-mediated Ca 2+ Channel MODULATION. Shapiro, Mark S., Jiuying Zhou and Bertil Hille. Department of Physiology and Biophysics, G424 Health Sciences Bldg., University of Washington, Box 357290, Seattle, Washington 98195-7290, USA.
APStracts 3:0034N, 1996.
1. We studied the effects of phorbol-12-myristate, 13-acetate (PMA) on G- protein-mediated inhibition of Ca 2+ channels by several neurotransmitters in rat superior cervical ganglion (SCG) sympathetic neurons, using the whole-cell patch clamp. PMA attenuated membrane-delimited inhibition of calcium currents (I Ca ) by norepinephrine (NE) and somatostatin by more than half, but did not attenuate inhibition by M 1 muscarinic receptors, which use a diffusible cytoplasmic messenger. Inhibition of I Ca by NE through PTX-sensitive and - insensitive G proteins was equally attenuated by PMA. PMA enhanced I Ca in about half the neurons (mean enhancement 10 +/- 1%) and strongly reduced the holding current in 44 of 61 cells. 2. The M-type K + current (I M ) was not suppressed by PMA, and PMA did not attenuate inhibition of I M by muscarinic agonists, which is also via a diffusible cytoplasmic messenger. 3. Attenuation of NE and SS inhibition by PMA was blocked by 1 [mu]M staurosporine, a broad- spectrum protein kinase inhibitor. Tests with three inhibitors selective for distinct isoforms of protein kinase C (PKC) gave mixed results. PMA actions were unaffected by 1 [mu]M calphostin C, blocked by 500 nM bisindolylmaleimide and unaffected by the pseudosubstrate inhibitor, PKC 19-36. . 4. Thus, we find that two membrane-delimited signaling pathways that inhibit ion channels in rat SCG neurons are strongly attenuated by PMA, but signaling pathway(s) that use a diffusible cytoplasmic messenger are not. We speculate that a non- standard PKC isoform, perhaps PKC[mu], mediates PMA actions.

Received 29 November 1995; accepted in final form 30 January 1996.
APS Manuscript Number J800-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 14 February 96