Contractile Responses to Histamine and GTPγS in β-Escin-Treated Skinned Smooth Muscle of Guinea Pig Ileum

Abstract

ABSTRACT-To characterize the calcium (Ca")-releasing effects of histamine and GTPrS, the drug-in duced tension developments were measured in (3-escin-treated skinned longitudinal smooth muscle of guinea pig ileum. Intracelluar Ca2+ stores were loaded with Ca" by incubating the muscle for 10 min in a Ca" containing solution. Histamine (10-100 pM), applied after Ca" -loading, produced a transient rise in ten sion. The effect of histamine was not preserved after treatment with 20 mM caffeine, a Ca2+-store releaser. The effect of histamine was potentiated by GTP; inhibited by GDP(3S, an antagonist of GTP for binding to G-proteins; or heparin, an antagonist of inositol 1,4,5-trisphosphate (IP3) for binding to its receptor; and mimicked by IP3. When GTPrS (20 ttM) was applied and continued to be present for 15 min, a transient rise in tension followed by a small, sustained rise in tension was elicited. The effect of GTPrS was completely inhibited by GDP(3S. The initial, transient component of the biphasic GTPrS response was abolished or markedly inhibited after treatment with caffeine, heparin or the calcium ionophore A23187. The present results suggest that histamine and GTPrS cause a release of Ca 21 from caffeine-sensitive stores which is mediated by IP3 formed through a G-protein-coupled mechanism. The GTPrS-induced Ca 2+ release is not considered to involve such an IP3-independent process as described in chemically-skinned arterial muscle.

Possible Involvement of a Small G-Protein Sensitive to Exoenzyme C3 of Clostridium botulinum in the Regulation of Myofilament Ca2+ Sensitivity in β-Escin Skinned Smooth Muscle of Guinea Pig Ileum

“…This is supported by the findings that GTPrS exerted a similar Ca"-sensitizing effect, and the effect was also inhibited by C3. GTPrS has been demonstrated to act on G-proteins that are implicated in muscarinic signaling mechanisms and mimic some muscarinic effects in intestinal smooth muscle such as an increase in myofilament Ca" sensitivity (5), release of internal Ca 21 stores (17,18,24) and activation of nonselective cationic current (17,25). To elaborate on the idea that muscarinic Ca2+-sensitization of tension development involves the small G-protein, further studies are needed to demonstrate that C3 induced ADP-ribosylation of the G-protein correlates with its inhibitory effect on CCh-induced tension development.…”

“…The muscle strip was mounted horizontally in a 0.3-m1 organ bath, with one end of the strip fixed on the black rubber bottom of the bath with a pin and the other attached to the thin lever of an isometric force transducer (TB-612T; Nihon Kohden, Tokyo), as previously described (18). The organ bath was filled with a physiological salt solution (PSS, composition given below) kept at 231C, and the muscle strip was equilibrated for 30-60 min under a tension of 150-180 mg.…”

“…Hirata et al (14) found that EDIN and C3 blocked GTPTS-induced Ca 21 sensitization of tension development and caused ADP-ribosylation of a rho p21-like protein in saponin-skinned arterial smooth muscle, and they suggested involvement of a member of the rho p21 family, rho A p21, in the Ca 21 sensitization. Current knowledge suggests that it would be attractive to test the possibility that Ca" -sensitizing effects of agonists can be blocked after ADP-ribosylation of the rho p21 small Gprotein, since GTPrS, which is a non-selective activator of G-proteins (15, 16), can mimic some of the agonist receptor-mediated effects (5,17,18) In the present study, the effect of C3 on carbachol (CCh)-induced Ca 21 sensitization of tension development was examined in (3-escin-skinned smooth muscle of …”

“…guinea pig ileum in which receptor-coupled signal transduction systems are well retained (18)(19)(20).…”

Pharmacological Modulation of Sarcoplasmic Reticulum Function in Smooth Muscle

“…This effect is mimicked, but with reduced potency, by other polyanions such as pentosan polysulfate and polyvinyl sulfate, suggesting that these agents act by increasing the local concentration of Ca 2ϩ near regulatory sites on the RyR-channel complex (Bezprozvanny et al, 1993). That this potentiating effect is relevant for smooth muscles, where RyR2 and/or RyR3 isoforms can be expressed instead of or in addition to RyR1, is evidenced by the fact that heparin (300 g/ml), which inhibits histamine (100 M)-and InsP 3 (40 M)-induced contractile activity, tends to potentiate subsequent caffeine (20 mM)-induced contractile activity in ␤-escin-permeabilized guinea pig ileum longitudinal smooth muscle layer (Fukami et al, 1993), although this effect could also be explained by a functional overlap of InsP 3 -and caffeinesensitive SR Ca 2ϩ stores. Heparin (300 g/ml) does not affect K ϩ (143 mM)-induced contractile activity in reversibly permeabilized rabbit ileum longitudinal smooth muscle layer (Kobayashi et al, 1988), suggesting that it does not affect Ca 2ϩ sensitivity of contractile proteins.…”