Selective disruption by protein kinases of G-protein-mediated Ca2+ channel modulation

J Neurophysiol. 1996 Jul;76(1):311-20. doi: 10.1152/jn.1996.76.1.311.


1. We studied the effects of phorbol-12-myristate, 13-acetate (PMA) on G-protein-mediated inhibition of Ca2+ channels by several neurotransmitters in rat superior cervical ganglion (SCG) sympathetic neurons, with the use of the whole cell patch clamp. PMA attenuated membrane-delimited inhibition of calcium currents (ICa) by norepinephrine (NE) and somatostatin by more than half, but did not attenuate inhibition by M1 muscarinic receptors, which use a diffusible cytoplasmic messenger. Inhibition of ICa by NE through pertussis-toxin-sensitive and -insensitive G proteins was equally attenuated by PMA. PMA enhanced ICa in about half the neurons (enhancement of 10 +/- 1%, mean +/- SE) and strongly reduced the holding current in 44 of 61 cells. 2. The M-type K+ current (IM) was not suppressed by PMA, and PMA did not attenuate inhibition of IM by muscarinic agonists, which is also via a diffusible cytoplasmic messenger. 3. Attenuation of NE and somatostatin inhibition by PMA was blocked by 1 microM staurosporine, a broad-spectrum protein kinase inhibitor. Tests with three inhibitors selective for distinct isoforms of protein kinase C (PKC) gave mixed results. PMA's actions were unaffected by 1 microM calphostin C, blocked by 500 nM bisindolylmaleimide, and unaffected by the pseudosubstrate inhibitor PKC19-36. 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 nonstandard PKC isoform, perhaps PKC mu, mediates PMA actions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium Channels / drug effects*
  • Cyclic AMP-Dependent Protein Kinases / drug effects
  • GTP-Binding Proteins / physiology*
  • Muscarinic Agonists / pharmacology
  • Neurons / drug effects*
  • Neurons / enzymology
  • Protein Kinase C / drug effects
  • Protein Kinases / drug effects*
  • Rats
  • Rats, Sprague-Dawley
  • Second Messenger Systems / drug effects
  • Signal Transduction / drug effects
  • Tetradecanoylphorbol Acetate / pharmacology*


  • Calcium Channels
  • Muscarinic Agonists
  • Protein Kinases
  • Cyclic AMP-Dependent Protein Kinases
  • Protein Kinase C
  • GTP-Binding Proteins
  • Tetradecanoylphorbol Acetate