Biochim Biophys Acta. 2003 Jul 23;1622(2):89-98
Barbar E, Rola-Pleszczynski M, Payet MD, Dupuis G.
Graduate Program in Immunology, Faculty of Medicine, University of Sherbrooke, QC, J1H 5N4, Sherbrooke, Canada
4-Aminopyridine (4AP) is a general blocker of voltage-dependent K(+) channels.
This pyridine derivative has also been shown to inhibit T cell proliferation, to modulate immune responses and to alleviate some of the symptoms associated with neurological disorders such as multiple sclerosis, myasthenia gravis and Alzheimer's disease.
4AP triggers a Ca(2+) response in lymphocytes, astrocytes, neurons and muscle cells but little is known about the regulation of the 4AP response in these cells.
We report that 4AP induced a non-capacitative transplasma membrane influx of Ca(2+) in Jurkat T lymphocytes.
The influx of Ca(2+) was not affected by activation or inhibition of protein kinase A (PKA).
In contrast, activation of protein kinase C (PKC) by phorbol myristyl acetate (PMA), mezerein or 1-oleoyl-2-acetyl-sn-glycerol (OAG) inhibited the influx of Ca(2+) triggered by 4AP.
The inhibitory effect of PKC could be prevented by prior exposure of the cells to the PKC inhibitor GF 109203X.
Under these conditions, mezerein and OAG no longer inhibited the 4AP-dependent Ca(2+) response.
Inhibition of serine and threonine protein phosphatases PP1 and PP2A by treating the cells with calyculin A (CalA) reduced the Ca(2+) response to 4AP.
Okadaic acid (OA) had no effect, suggesting an involvement of PP1.
A combination of CalA and OAG (or PMA) abolished the influx of Ca(2+) induced by 4AP, adding further evidence to the importance of protein phosphorylation in the modulation of the 4AP response.
Our data suggest that the transplasma membrane influx of Ca(2+) triggered by 4AP in Jurkat T cells can be modulated by the opposite actions of PKC and protein serine and threonine phosphatase(s).