Neuronal cells grown in culture were exposed to drugs that stimulate protein kinase C (phorbol myristate acetate), inhibit the catalytic site in protein kinase C (H7, staurosporine) or inhibit the regulatory site in protein kinase C (calphostin, sphingosine). In NG-108 and N1E-115 cells, phorbol myristate acetate produced substantial stimulation of protein kinase C activity (0.1 μM produced ~75% stimulation). In these same cells, H7 [100% inhibition concentration (IC100) ~1 mM] and staurosporine (IC100 ~0.2 μM) inhibited the catalytic site in the enzyme, and calphostin (IC80-IC90 ~2.0 μM) and sphingosine (IC80-IC90 ~1 μM) inhibited the regulatory site in the enzyme. Phorbol myristate acetate, as well as drugs that inhibit the catalytic and regulatory sites in protein kinase C, were tested for their effects on phrenic nerve-hemidiaphragm preparations. At concentrations that stimulated enzyme activity in neuronal cells in culture, phorbol myristate acetate did not augment normal transmission, nor did it restore transmission to preparations bathed in medium with low calcium (0.4-0.6 mM). At concentrations equivalent to the IC80 to IC100 values in neuronal cells in culture, H7, staurosporine, calphostin and sphingosine did not paralyze short-term transmission, nor did they depress transmission in tissues bathed in low calcium. Pretreatment of neuromuscular preparations with phorbol myristate acetate, H7, staurosporine, calphostin or sphingosine did not alter the amount of time necessary for botulinum neurotoxin type A, botulinum neurotoxin type B or tetanus toxin to paralyze transmission. The data indicate that protein kinase C is not required for short-term neuromuscular transmission. The results also indicate that protein kinase C cannot be the target for clostridial toxins or any other toxins that act acutely to block neuromuscular transmission.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Dec 1 1992|
ASJC Scopus subject areas
- Molecular Medicine