Protein kinase C evokes quantal catecholamine release from PC12 cells via activation of L-type Ca2+ channels.
Application of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) to PC12 cells under resting conditions evoked quantal catecholamine secretion, as detected amperometrically. This effect was not mimicked by 4alpha-phorbol-12,13-didecanoate, another phorbol ester, which is inactive with respect to protein kinase C activation, and was prevented by the protein kinase C inhibitor bisindolylmaleimide. TPA also caused a rise of [Ca(2+)](i) in Fura-2-loaded PC12 cells, and again this was not mimicked by 4alpha-phorbol-12,13-didecanoate and could be blocked by bisindolylmaleimide. TPA-evoked secretion was entirely dependent on extracellular Ca(2+) and was fully abolished by nifedipine, as were TPA-induced rises of [Ca(2+)](i). Resting membrane potential, monitored using perforated patch recordings, was unaffected by TPA. However, a small (6-8 mV) hyperpolarizing shift in the voltage dependence of Ca(2+) channel currents (determined using whole-cell patch clamp recordings) was induced by TPA, and this could be fully prevented by nifedipine. In contrast to results with depolarizing stimuli, which evoke exocytosis because of Ca(2+) influx through N-type channels in these cells, the present results indicate that protein kinase C activation leads directly to quantal catecholamine secretion in the absence of depolarizing stimuli via a selective shift in the activation of L-type Ca(2+) channels.
Taylor
S C
SC
Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, United Kingdom.
Green
K N
KN
Carpenter
E
E
Peers
C
C
D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D004563:Electrochemistry; D004789:Enzyme Activation; D008564:Membrane Potentials; D016716:PC12 Cells; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D020746:Calcium Channels, L-Type; D002395:Catecholamines; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate