Direct activation of Ca2+ channels by palmitoyl carnitine, a putative endogenous ligand

Br J Pharmacol. 1987 Oct;92(2):457-68. doi: 10.1111/j.1476-5381.1987.tb11343.x.


1 Palmitoyl carnitine, a lipid metabolite which accumulates in cytoplasmic membranes during ischaemia, has been shown to resemble the Ca2+ channel activator, Bay K 8644, in K+-depolarized smooth muscle. Palmitoyl carnitine caused concentration-dependent (1-1000 mumol l-1) augmentations in the sensitivity to Ca2+ of K+-depolarized taenia preparations from the guinea-pig caecum. The (+/-)-isomer was equieffective with the (-)-isomer, whereas carnitine was ineffective and palmitic acid relaxed the tissues. The shift to the left of Ca2+ concentration-response curves induced by palmitoyl carnitine (100 mumol l-1) was additive with that of Bay K 8644 (1 mumol l-1). 2 The interactions of palmitoyl carnitine with the different classes of calcium-antagonist were similar to those seen with Bay K 8644. Schild plots of the calcium-antagonist effects of nifedipine were shifted to the right following preincubation of the taenia with palmitoyl carnitine (30-300 mumol l-1). The inhibitory effects of verapamil were especially sensitive to palmitoyl carnitine (100 mumol l-1). Whereas the potency of diltiazem as a calcium-antagonist was reduced by palmitoyl carnitine (100 mumol l-1), the inhibitory effects of the lipophilic class III calcium-antagonists, cinnarizine and flunarizine, were entirely resistant to palmitoyl carnitine (100 mumol l-1). 3 Although palmitoyl carnitine has detergent properties in high concentrations and lyses red blood cells, these effects were not Ca2+-dependent, nor were they modified by calcium-antagonists. Other detergents did not have selective interactions with Ca2+ channels. 4 Palmitoyl carnitine inhibited [3H]-nitrendipine, [3H]-verapamil and [3H]-diltiazem binding to rat cortical membranes with IC50 values (mumol l-1) of 120 +/- 1, 95 +/- 17 and 120 +/- 15 mumol l-1 respectively. The inhibition showed little temperature-dependence, in contrast to that of Bay K 8644, except for a small reduction in the IC50 value for [3H]-verapamil binding at 37 degrees C (42 +/- 5 mumol l-1). Palmitoyl carnitine interacted selectively with the Ca2+ channel, in that effects on ligand binding to alpha-adrenoceptors, beta-adrenoceptors and 5-HT1A receptors occurred only at 5-10 fold higher concentrations. 5 It is concluded that palmitoyl carnitine, at concentrations which have previously been shown to occur in the cytoplasm during myocardial ischaemia, may interact directly with Ca2+ channels and may therefore be considered as an endogenous modulator of channel function. The site of action differs from that of other agents.

MeSH terms

  • Animals
  • Binding, Competitive / drug effects
  • Calcium Channel Blockers / pharmacology
  • Carnitine / analogs & derivatives*
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism
  • Detergents / pharmacology
  • Guinea Pigs
  • In Vitro Techniques
  • Ion Channels / drug effects*
  • Male
  • Membranes / drug effects
  • Membranes / metabolism
  • Muscle, Smooth / drug effects
  • Palmitoylcarnitine / pharmacology*
  • Rats
  • Rats, Inbred Strains
  • Verapamil / metabolism


  • Calcium Channel Blockers
  • Detergents
  • Ion Channels
  • Palmitoylcarnitine
  • Verapamil
  • Carnitine