Direct block of calcium channels by dioctanoylglycerol in pregnant rat myometrial cells
Kusaka, M.; Sperelakis, N.
Molecular Pharmacology 47(4): 842-847
1995
ISSN/ISBN: 0026-895X PMID: 7723746 Document Number: 442125
The effect of 1,2-dioctanoyl-sn-glycerol (DiC8), a diacylglycerol and potent protein kinase C (PKC) activator, on the voltagedependent slow (L-type) Ca-2+ current (I-Ca(L)) was examined using whole-cell voltage clamp of myometrial cells freshly isolated from late pregnant rats. Bath application of DiC8 (25 mu-M) decreased I-Ca(L) by 50.7 +- 2.4% (n = 22). The effect was reversible and dose dependent (IC-50 of 15.3 mu-M). The effect of DiC8 was not reversed or prevented by application of calphostin C, a selective PKC inhibitor. In addition, 1-oleoyl-2-acetyl-sn-glycerol, another PKC activator, did not produce an inhibitory effect on I-Ca(L), even at a concentration of 100 mu-M; I-Ca(L) was actually slightly stimulated (10.6 +- 5.1%, n = 6). The steady state inactivation curve for I-Ca(L) was shifted to the left by DiC8 application (by approximately 15 mV at 25 mu-M), whereas the activation curve was not affected; the shift should produce a voltage-dependent block. DiC8 decreased I-Ca(L) progressively during repetitive step depolarizations (use-dependent block). We conclude from these results that (a) DiC8 inhibits I-Ca(L) independently of PKC in uterine muscle cells and (b) DiC8 preferentially acts on the inactivated state and/or open state of the L-type Ca-2+ channels. Therefore, caution must be exercised when studying PKC actions on ion channel regulation using DiC8 as a PKC activator.