Different pathways of calcium sensitization activated by receptor agonists and phorbol esters in vascular smooth muscle

Developmental changes in response to endothelins and receptor subtypes of isolated rat duodenum

The response of isolated duodenum to endothelin-1, -3 and IRL 1620 (Suc-[Glu9,Ala11,15]endothelin-1 (8-21)), a selective endothelin ETB receptor agonist, was studied in both neonatal (1-week-old) and adult rats by recording mechanical activity isotonically. Endothelin-1, -3 and IRL 1620 (1-100 nM) elicited sustained contraction of neonatal duodenum, in a concentration-dependent manner, with a potency order of endothelin-1 = endothelin-3 > IRL 1620. The response to endothelin-1 and -3 (10-1000 nM) of adult duodenum was biphasic, i.e., transient relaxation followed by contraction, with a potency order of endothelin-1 > endothelin-3. The contractile response to endothelin-1 of adult but not neonatal duodenum was significantly antagonized by pretreatment with FR139317 (1 microM), an endothelin ETA receptor antagonist. An endothelin ETB receptor antagonist, RES-701-1 (3 microM), weakly antagonized the IRL 1620-induced contraction of neonatal duodenum. However, RES-701-1 (10 microM) did not affect the response to endothelin-1 of either adult or neonatal duodenum. These results indicate that the duodenal response to endothelins changes from a sustained contraction in neonates to a biphasic response in adults. The contractile response to endothelins of neonatal duodenum is suggested to be mediated through endothelin ETB receptors or possibly RES-701-1-resistant ETB receptor subtypes and contraction of adult duodenum through endothelin ETA receptors. The mechanism of the endothelin-induced response of duodenum was also studied.

Possible involvement of a small G-protein sensitive to exoenzyme C3 of Clostridium botulinum in the regulation of myofilament Ca2+ sensitivity in beta-escin skinned smooth muscle of guinea pig ileum

The effects of exoenzyme C3 of Clostridium botulinum on Ca(2+)- and drug-induced tension developments were investigated in beta-escin skinned smooth muscle of guinea pig ileum to test the involvement of a small G-protein in the regulation of myofilament Ca2+ sensitivity. C3 is known to ADP-ribosylate the rho p21 family of small G-proteins. Treatment with C3 (0.35 microgram/ml, for 30 min) shifted the pCa-tension curve rightward along the Ca2+ concentration axis, indicating a decrease in Ca2+ sensitivity of the contractile elements. The inhibitory effect of C3 was not preserved after treatment with GDP beta S (1 mM), an antagonist of GTP for the binding to G-proteins. Stimulation of muscarinic receptors with carbachol (CCh, 100 microM) shifted the pCa-tension curve leftward, indicating Ca2+ sensitization of tension development. The Ca(2+)-sensitizing effect of CCh was not observed after C3 treatment. When GTP gamma S (10 microM), an activator of G-proteins, was applied at a plateau of tension development produced by a moderate concentration of Ca2+, further increase in tension was elicited and the effect of GTP gamma S was inhibited by C3 treatment. The results suggest the possible involvement of a rho p21-like small G-protein in the regulation of Ca2+ sensitivity of smooth muscle myofilaments.

Differences in sensitivity to the specific protein kinase C inhibitor Ro31-8220 between small and large bronchioles of the rat

1. The involvement of protein kinase C (PKC) in constriction of small bronchioles has never been investigated. In this study we have examined the effects of the specific PKC inhibitors Ro31-8220 and Ro31-7549 and the non-specific inhibitor H7 on carbachol-, 5-hydroxytryptamine (5-HT)- and 4 beta-phorbol dibutyrate (4 beta-PDBu)-induced contractions in large and small bronchioles. 2. The study was performed on isolated bronchioles of the rat with internal diameters of 574 microns +/- 11 (small, n = 128), and 1475 microns +/- 32 (large, n = 93), using a Mulvaney-Halpen small vessel myograph. 3. In these preparations 4 beta-PDBu had no effect if added on its own. However, after precontracting with 30 mM K+, 0.5 microM 4 beta-PDBu caused a contractile response of 110.4 +/- 7.0% TK (TK = maximum response to 75 mM K+ in small and 69.3 +/- 6.5% TK in large bronchioles. Ro31-8220, Ro31-7549 and H7 all showed concentration-dependent inhibition of this response. 4. In small bronchioles 10 microM Ro31-8220 shifted both the carbachol and 5-HT concentration-response curves to the right, and reduced the maximum response. In contrast, 10 microM Ro31-8220 had no significant effect on the EC50 to carbachol of larger bronchioles, although the maximum response was reduced, and had no significant effect on the 5-HT concentration-response curve. 200 microM H7 shifted the carbachol concentration--response curve to the right as well as reducing the maximal response in both small and large bronchioles. 5 Large bronchioles exhibited a greater rate of decay of carbachol-induced contraction than did small bronchioles. Pretreatment with Ro31-8220 accelerated the rate of decay.6 Pretreatment with 10 JM Ro3l-8220 caused a small reduction in the response to 75 mM K+ in both small and large bronchioles (small: to 87.8 +/- 3.0% TK; large: to 94.1 +/- 0.8% TK). H7 at 200 JM caused a much larger reduction in both preparations (small: to 75.1 +/- 3.0% TK); large: to 82.7 +/- 0.6% TK).7 Small bronchioles were more sensitive than larger bronchioles to agonists and phorbol ester. The protein kinase inhibitor Ro31-8220 could reduce agonist-induced constriction in small and large bronchioles,as well as reducing or abolishing phorbol ester-induced contractions. Small bronchioles were more sensitive than large bronchioles to Ro31-8220. These results suggest that there is a significant PKC involvement in constriction of bronchioles to carbachol and 5-HT, and that the proportion of the contractile response that can be attributed to PKC is greater in smaller than larger bronchioles.

Inhibitory effects of quercetin and staurosporine on phasic contractions in rat vascular smooth muscle

The aim of this work was to analyze the effects of quercetin and staurosporine on the phasic contractile responses in rat aorta induced by noradrenaline, 5-hydroxytryptamine (5-HT, serotonin) and caffeine in Ca(2+)-free media. Both quercetin and staurosporine inhibited the contractions induced by 10(-5) M noradrenaline, 10(-5) M 5-HT and 20 mM caffeine in Ca(2+)-free solution. Phorbol 12-myristate 13-acetate (5 x 10(-8) M) enhanced this transient contraction elicited by noradrenaline, an effect that was abolished by quercetin (5 x 10(-5) M). The relaxant effects of quercetin on 80 mM KCl induced contractions were similar in normal and low Na+ solution, e.g. when Ca2+ efflux through the Na+/Ca2+ exchanger was inhibited. Furthermore, quercetin or staurosporine had no effect on 45Ca2+ efflux under resting conditions or when stimulated by 10(-5) M noradrenaline. These results suggested that the inhibitory effects of quercetin and staurosporine on phasic contractile responses induced by receptor agonists in Ca(2+)-free media do not seem to be related to changes in cellular Ca2+ regulation but to an inhibitory effect on the regulation of contractile proteins, an effect probably related to the decreased sensitivity of contractile elements to Ca2+ that apparently resulted from the inhibitory effects of quercetin and staurosporine on protein kinases.