Korean J Physiol Pharmacol.  2008 Feb;12(1):31-35. 10.4196/kjpp.2008.12.1.31.

Lysophosphatidylcholine Increases Ca2+ Current via Activation of Protein Kinase C in Rabbit Portal Vein Smooth Muscle Cells

• Jung S
• Lee Y
• Han S
• Kim Y
• Nam T
• Ahn D

• KMID: 2071643
• DOI: http://doi.org/10.4196/kjpp.2008.12.1.31

Abstract

Lysophosphatidylcholine (LPC), a metabolite of membrane phospholipids by phospholipase A(2), has been considered responsible for the development of abnormal vascular reactivity during atherosclerosis. Ca2+ influx was shown to be augmented in atherosclerotic artery which might be responsible for abnormal vascular reactivity. However, the mechanism underlying Ca2+ influx change in atherosclerotic artery remains undetermined. The purpose of the present study was to examine the effects of LPC on L-type Ca2+ current (ICa(L)) activity and to elucidate the mechanism of LPC-induced change of ICa(L) in rabbit portal vein smooth muscle cells using whole cell patch clamp. Extracellular application of LPC increased ICa(L) through whole test potentials, and this effect was readily reversed by washout. Steady state voltage dependency of activation or inactivation properties of ICa(L) was not significantly changed by LPC. Staurosporine (100 nanometer) or chelerythrine (3 micrometer, which is a potent inhibitor of PKC, significantly decreased basal ICa(L), and LPC-induced increase of ICa(L) was significantly suppressed in the presence of PKC inhibitors. On the other hand, application of PMA, an activator of PKC, increased basal ICa(L) significantly, and LPC-induced enhancement of ICa(L) was abolished by pretreatment of the cells with PMA. These findings suggest that LPC increased ICa(L) in vascular smooth muscle cells by a pathway that involves PKC, and that LPC-induced increase of ICa(L) might be, at least in part, responsible for increased Ca2+ influx in atherosclerotic artery.

Keyword

Lysophosphatidylcholine; Ca2+ current; Protein kinase C; Vascular smooth muscle

MeSH Terms

Arteries
Atherosclerosis
Benzophenanthridines
Dependency (Psychology)
Hand
Lysophosphatidylcholines
Membranes
Muscle, Smooth
Muscle, Smooth, Vascular
Myocytes, Smooth Muscle
Phospholipases
Phospholipids
Portal Vein
Protein Kinase C
Protein Kinases
Staurosporine
Benzophenanthridines
Lysophosphatidylcholines
Phospholipases
Phospholipids
Protein Kinase C
Protein Kinases
Staurosporine

Figure

• 

  Fig. 1. (A) Plot of Ca2+ currents evoked by repetitive step depolarization from −80 mV to 0 mV versus time. Horizontal bar indicates the time of LPC (1 μM), and nifedipine (1 μM) application in the bath. (B) Summary of the LPC-induced change of ICa(L). The value of LPC-induced change was expressed as % of control. Bath application of LPC increased the current amplitude to 142.6±8.4% (n=19). (C) Effect of LPC on current-voltage relations of ICa(L). ICa(L) was recorded at 10 mV increments between −50 and +60 mV from a holding potential of −80 mV. (D) Summary of voltage dependence of ICa(L) for control (○), 1 μM LPC (•), and 1 μM nifedipine. At each voltage steps, peak values of current were determined, and averaged (n=8).

• 

  Fig. 2. Steady state activation and inactivation curves of ICa(L) obtained before and after LPC application. (A) Steady state activation curves of ICa(L) in control and LPC. Chord conductance (G) was measured at different membrane potentials and normalized to the maximal chord conductance (Gmax). Each data points were the means of 8 experiments and fitted using a following form of Boltzman equation; Y={1+exp[(V1/2 – V)/k]}−1, where V1/2 represents half maximal activation potential and k is slope factor. Measured V1/2 was −5.8±0.2 mV and −3.1±0.1 mV in control and LPC, respectively. (B) Steady state inactivation curves of ICa(L) in control and LPC. Current amplitudes (I) of test potential to 0 mV from different pretest potentials were normalized to the maximal current (Imax). Each data points were the means of 6 experiments. Curves were obtained from following form of Boltzman equation; Y={1+exp[(V – V1/2)/k]}−1, where V1/2 represents half maximal inactivation potential and k is slope factor. V1/2 was −31.4±1.2 mV and −30.2±1.6 mV in control and LPC, respectively.

• 

  Fig. 3. Effect of PKC on LPC-induced change of ICa(L). Plot of Ca2+ currents evoked by repetitive step depolarization from −80 mV to 0 mV versus time. Temporal course of change of ICa(L) during treatment of LPC (1 μM) alone and LPC with 3 μM chelerythrine (A), or with 100 nM PMA (B). Horizontal bars indicate the time of drugs application. (C) Summary of the effect of pretreatment of staurosporine (100 nM), chelerythrine (3 μM), and PMA (100 nM) on LPC-induced change of ICa(L). Data are expressed as the % of control. Number of cells in each experimental condition is indicated in parenthesis.

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