The late Na+ current (INa) inhibitor ranolazine attenuates effects of palmitoyl-L-carnitine to increase late INa and cause ventricular diastolic dysfunction.

Palmitoyl-L-carnitine (PC), an ischemic metabolite, causes cellular Na(+) and Ca(2+) overload and cardiac dysfunction. This study determined whether ranolazine [(+/-)-1-piperazineacetamide, N-(2,6-dimethylphenyl)-4-[2-hydroxy-3-(2-methoxyphenoxy)propyl]-] attenuates PC-induced Na(+) current and ventricular contractile dysfunction of the isolated heart. PC (4 microM, 30 min) increased late Na(+) current by 1034 +/- 349% in guinea pig isolated ventricular myocytes; ranolazine (10 microM) and tetrodotoxin (TTX, 3 microM) significantly attenuated this effect of PC. PC increased left ventricular end-diastolic pressure (LVEDP), coronary perfusion pressure (CPP), wall stiffness, and cardiac lactate and adenosine release from the isolated heart. Ranolazine (10 microM) significantly reduced the PC-induced increase in LVEDP by 72 +/- 6% (n = 6, p < 0.001), reduced left ventricular wall stiffness, and attenuated the PC-induced increase of CPP by 53 +/- 10% (n = 6-7, p < 0.05). Ranolazine (10 microM) reduced the PC-induced increases of lactate and adenosine release by 70 +/- 8 and 81 +/- 5%, respectively (n = 6, p

[Destabilization of the cytosolic calcium level and cardiomyocyte death in the presence of long-chain fatty acid derivatives].

It has been shown using the fluorescent microscopy technique that long-chain fatty acid derivatives, myristoylcarnitine and palmitoylcarnitine, exert the most toxic effect on rat ventricular cardiomyoctes. The addition of 20-50 microM acylcarnitines increases calcium concentration in cytoplasm ([Ca2+]i) and causes cell death after the 4-8 min lag-period. This effect is independent on extracellular calcium and L-type calcium channel inhibitors. Free acids (myristic and palmitic acids) at a concentration of 300-500 microM have a little effect on [Ca2+]i within 30 min. We suggest that the toxic effect is due to the activation of sarcoplasmic reticulum calcium channels by acylcarnitines and resulting acyl-CoA. Mitochondria play a role of calcium-buffer system in these conditions. The calcium capacity of this buffer determines the lag-period. Phosphate increases the calcium capacity of mitochondrial and the lag-period. In the presence of rotenone and oligomycin the elevation of [Ca2+]i after the addition of acylcarnitines occurs without the lag-period. The exhaustion of the mitochondrial calcium-buffer capacity or significant depolarization of mitochondrial leads to a rapid release of calcium from mitochondria and cell death. Thus, the activation of reticular calcium channels is the main reason of the toxicity of myristoylcarnitine and palmitoylcarnitine.

Dodecylphosphocholine-mediated enhancement of paracellular permeability and cytotoxicity in Caco-2 cell monolayers.

The intestinal epithelium is a significant barrier for oral absorption of hydrophilic drugs because they cannot easily traverse the lipid bilayer of the cell membrane and their passage through the intercellular space (paracellular transport) is restricted by the tight junctions. In this report we show that dodecylphosphocholine (DPC) can improve the paracellular permeability of hydrophilic compounds across Caco-2 cell monolayers by modulating the tight junctions. The results show that the alkyl chain as well as the zwitterionic head group of DPC are required for its activity. DPC appears to act by modulating the permeability of tight junctions as evidenced by the fact that treatment of Caco-2 cell monolayers by this agent results in a decreased transepithelial electrical resistance (TEER), increased permeability of paracellular markers (e. g., mannitol) with no change in the permeability of the transcellular marker testosterone, and redistribution of the tight junction-associated protein ZO-1. The effect of DPC on Caco-2 cells (e.g., decrease in TEER) is reversible, and is not caused by gross cytotoxicity (as indicated by the MTT test) or by nonspecific disruption of the cell membrane (as indicated by only slight nuclear staining due to the nonpermeable DNA-specific dye propidium iodide). We propose in the present study a parameter, potency index, that allows comparison of various enhancers of paracellular transport in relation to their cytotoxicity. The potency index is a ratio between the IC(50) value (concentration at which 50% inhibition of control mitochondrial dehydrogenase activity occurs in the MTT test) and the EC(50) value (concentration at which TEER drops to 50% of its control (untreated) value). By this parameter, DPC is significantly safer than the commonly used absorption enhancer palmitoyl carnitine (PC), which has the potency index of approximately 1 (i.e., no separation between effective and toxic concentration).

Lidocaine attenuates mechanical and metabolic derangements induced by palmitoyl-L-carnitine in the isolated perfused rat heart.

The effect of lidocaine on the palmitoyl-L-carnitine (PALCAR)-induced mechanical and metabolic derangements was studied in Langendorff rat hearts, perfused aerobically at a constant flow rate and paced electrically. PALCAR (5 mumol/l) increased the left ventricular end-diastolic pressure, decreased the left ventricular developed pressure (i.e., mechanical dysfunction), and decreased the tissue levels of adenosine triphosphate and creatine phosphate (i.e., metabolic change). These mechanical and metabolic alterations induced by PALCAR were concentration-dependently attenuated by lidocaine (20, 50 or 100 mumol/l). Nevertheless, lidocaine (20, 50 or 100 mumol/l) did not affect the mechanical function and energy metabolism of the normal (PALCAR-untreated) heart. These results indicate that lidocaine has a cardioprotective action against the PALCAR-induced mechanical and metabolic derangements.

Protective effects of dilazep and its derivative K-7259 on the haemolysis induced by amphiphiles in rat erythrocytes.

The effects of dilazep and K-7259, a dilazep derivative, on the haemolysis (as evidenced by release of haemoglobin) induced by palmitoyl-L-carnitine (PAL-CAR) or palmitoyl 1-alpha-lysophosphatidylcholine (PAL-LPC) have been determined in rat erythrocytes. At concentrations above the critical micelle concentration both PAL-CAR and PAL-LPC induced haemolysis; the concentrations of PAL-CAR and PAL-LPC producing 50% haemolysis were approximately 13 and 14 microM, respectively. The 50% haemolysis induced by PAL-CAR or PAL-LPC was attenuated by dilazep (1, 10 or 100 microM) but not at the highest concentration used (1 mM). K-7259 attenuated the 50% haemolysis induced by PAL-CAR or PAL-LPC at concentrations ranging from 1 microM to 1 mM. Similarly, dilazep (1 to 100 microM) and K-7259 (1 microM to 1 mM) significantly or insignificantly attenuated the 25% and 75% haemolysis induced by PAL-CAR or PAL-LPC. Neither dilazep nor K-7259 affected micelle formation by PAL-CAR or PAL-LPC, nor, at concentrations of 1 and 10 microM, did they attenuate the haemolysis induced by osmotic imbalance (hypotonic haemolysis). These results suggest that both dilazep and K-7259 protect the erythrocyte membrane from the damage induced by PAL-CAR or PAL-LPC. The protective effects of dilazep and K-7259 are mediated by some mechanism other than prevention of micelle formation or protection of the erythrocyte membrane against osmotic imbalance.