Effects of arachidonic acid on voltage-gated Ca channel current in single smooth muscle cells isolated from guinea pig vas deferens.

Effects of arachidonic acid (AA) and related fatty acids on Ca2+ -independent transient (A-type) K+ current (I(A)) were examined in single myocytes of guinea pig vas deferens, ureter, and proximal colon as well as in rabbit vas deferens. The peak amplitude of I(A) was reduced by external application of AA (half-maximal inhibitory concentration = approximately 1 microM). The blocking effect was not changed significantly by indomethacin, nordihydroguaiaretic acid, guanosine 5'-O-(2-thiodiphosphate), or guanosine 5'-O-(3-thiotriphosphate). Pharmacological studies suggested that the effect of AA was not mediated by activation of protein kinases A or C or tyrosine kinase. AA (20:4) was the most potent of the four types of cis-eicosanoic acids with two to five double bonds (20:2 to 20:5) that were tested. I(A)-like current in cardiac atrial myocytes of the rabbit was not affected significantly by 30 microM AA. These results indicate that AA itself directly blocks A-type K+ channels. A relationship between stereospecific chemical structure of fatty acids and their blockade of A-type K+ channels is suggested. A-type K+ channels in smooth muscle cells can be clearly resolved from those in atrial myocytes by the responses to AA.

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Mechanisms of NE-induced reduction of Ca current in single smooth muscle cells from guinea pig vas deferens

AJP Cell Physiology ◽

10.1152/ajpcell.1991.260.1.c17 ◽

1991 ◽

Vol 260 (1) ◽

pp. C17-C25 ◽

Cited By ~ 48

Author(s):

Y. Imaizumi ◽

M. Takeda ◽

K. Muraki ◽

M. Watanabe

Keyword(s):

Smooth Muscle ◽

Guinea Pig ◽

Smooth Muscle Cells ◽

Vas Deferens ◽

Muscle Cells ◽

Ca Channel ◽

Patch Clamp Technique ◽

Small Shift ◽

Simultaneous Application ◽

Pipette Solution

Effects of norepinephrine (NE) on voltage-dependent Ca channel current (ICa) were examined applying whole cell patch-clamp technique to single smooth muscle cells freshly isolated from vas deferens of the guinea pig. K currents and contraction of the cell were abolished by Cs and EGTA in the pipette solution, respectively. The peak ICa and Ba current (IBa) elicited by depolarization from -60 mV in a solution containing 2.2 mM Ca or Ba were reduced by 10-60% in voltage- and dose-dependent manners by the application of NE or phenylephrine. This effect was greatly attenuated in the presence of prazosin. The decrease in IBa was always smaller than that in ICa at any potential. Even after simultaneous application of 5 mM caffeine and 10 microM NE to the cells in a Ba-containing solution, the second challenge with NE again reduced IBa in a similar manner. The decrease in IBa by 10 microM NE could not be explained well by a small shift (-5 mV) of the voltage dependence of the steady-state inactivation. The effect of NE on IBa was irreversibly enhanced by 0.1 mM guanosine 5'-O-(3-thiotriphosphate) and almost abolished by 1 mM guanosine 5'-O-(2-thiodiphosphate) added to the pipette solution but appeared not to be affected by the treatment with pertussis toxin. It can be concluded that, under these experimental conditions, the activation of alpha 1-adrenoceptor in vas deferens smooth muscle cells reduces Ca channel activity possibly via a mechanism involving GTP-binding protein in addition to Ca-mediated Ca channel inactivation mechanism.

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