MODULATION OF CALCIUM-CHANNEL CURRENTS BY ARACHIDONIC-ACID IN SINGLE SMOOTH-MUSCLE CELLS FROM VAS-DEFERENS OF THE GUINEA-PIG

1 Effects of arachidonic acid (AA) on voltage-dependent Ca channel currents were investigated by whole-cell-clamp methods in single smooth muscle cells freshly isolated from vas deferens of the guineapig. 2 Ca channel current was decreased by application of 1-30 mu M AA in a concentration-dependent manner. When Ca2+ or Ba2+ was the charge carrier, Ca channel current (I-Ca or I-Ba) was reduced by AA to a similar extent (IC50 = 10 and 6 mu M, respectively). Addition of 15 mM BAPTA to the pipette solution did not affect the reduction of I-Ba by 10 mu M AA. 3 The effect of AA on I-Ba was not prevented by internal application of 1 mM nordihydroguaiaretic acid (NDGA) and 1 mM. indomethacin (Indo). When the pipette solution contained 0.1 mM guanosine-5'-triphosphate (GTP), I-Ba was decreased slightly but significantly by application of 30 mu M prostaglandin F-2 alpha FGF)(2 alpha) but not by PGE(2). This effect of PGF(2 alpha) was irreversible or not observed when the pipette solution contained 0.3 mM guanosine-5'-(3-thiotriphosphate) (GTP gamma S) or both GTP or guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), respectively. 4 External application of 100 units ml(-1) superoxide dismutase slightly but significantly attenuated the inhibition of I-Ba by 1-30 I IM AA. Intracellular application of 1 mM GDP beta S or 0.3 mM GTP gamma S did not significantly change the effect of AA. Intracellular application of 0.1 mM 1-(5-isoquinolinesulphonyl)-2-methylepiperazine (H-7) also did not change the effect of AA. 5 These results indicate that the decrease in Ca channel currents in vas deferens smooth muscle cells is mainly due to AA itself, as opposed to its metabolites. The effect of AA may be due to AA itself, as opposed to its metabolites. The effect of AA may be due to its direct action on Ca channels or membrane phospholipids, but may not be mediated by activation of GTP binding proteins or protein kinase C. The inhibition of Ca channel current by AA may be partly induced by superoxide radicals derived from AA oxidation. PGF(2 alpha) also reduces Ca channel currents but probably by a separate mechanism via activation of a GTP binding protein.