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J Ren, E Karpinski and CG Benishin
Department of Physiology, Faculty of Medicine, University of Alberta, Edmonton, Canada.
There is evidence to suggest that PGE2 plays an important role in the regulation of vascular smooth muscle tone. To determine the cellular basis of this action, we studied the effect of PGE2 on force in helical muscle strips from rat tail artery. PGE2 evoked a sustained contractile response. The contractile response was concentration-dependent, with an EC50 value of 9.6 microM. Patch-clamp studies were conducted to investigate the effects of PGE2 on K channels in isolated vascular smooth muscle cells from rat tail artery. Current-clamp studies showed that PGE2 (1 microM) depolarized the membrane by 15.9 +/- 1.3 mV. Under voltage-clamp conditions, a voltage-dependent, delayed outward rectifier K current was generated by stepwise depolarization from a holding potential of -80 mV. The current, which was activated at -45 to -40 mV and showed almost no inactivation, was inhibited by 45% using 10 mM TEA. PGE2 inhibited the outward K current in a concentration- dependent manner, with EC50 values of 3.5 microM and 4.9 microM in primary and subcultured cells, respectively. The PGE2 receptor antagonist sodium meclofenamate abolished the PGE2-induced K current inhibition. Furthermore, the intracellular application of guanosine 5'- O(-)[2-thiodiphosphate] (GDP beta S), a G protein inhibitor, and pretreatment of the cells with cholera toxin prevented the PGE2-induced inhibition, whereas application of pertussis toxin did not.(ABSTRACT TRUNCATED AT 250 WORDS)
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