Guanine nucleotide‐ and inositol 1,4,5‐trisphosphate‐induced calcium release in rabbit main pulmonary artery.

Abstract

1. The effects of activation of guanine nucleotide‐binding protein (G protein) by guanine nucleotides or sodium fluoride on the release of intracellular Ca2+ and on tension development were determined in chemically skinned strips of rabbit main pulmonary arteries (MPA). Ca2+ movements were monitored with Fura‐2, as the change in free Ca2+ concentration in the bath medium surrounding the skinned MPA. 2. Sodium fluoride or non‐hydrolysable analogues of GTP, guanosine 5'‐[gamma‐thio]triphosphate (GTP gamma S) and guanosine 5'‐[beta,gamma‐imido]triphosphate (GMP‐PNP), induced sustained and dose‐dependent contraction of skinned MPA. GTP (100 microM) induced transient contraction of skinned MPA. GTP gamma S did not contract intact MPA. We also confirmed that inositol 1,4,5‐trisphosphate (InsP3) released sufficient Ca2+ to induce contraction of skinned, but not intact, MPA. 3. Guanosine 5'‐[beta‐thio]diphosphate (GDP beta S), a non‐hydrolysable analogue of GDP that competitively inhibits the binding of guanine nucleotides to G proteins, inhibited the contractions induced by GTP gamma S. Neomycin (1 mM) inhibited the GTP gamma S‐induced contractions, but also, to a lesser extent, contractions induced by caffeine. 4. Depletion of Ca2+ from the sarcoplasmic reticulum (SR) or treatment with Triton X‐100 inhibited the GTP gamma S‐induced contractions. The effects of Ca2+ depletion was reversible, while that of Triton X‐100 was irreversible. GTP gamma S (up to 100 microM) had no apparent effect on the pCa‐tension curve of freeze‐glycerinated MPA. 5. GTP gamma S‐ or InsP3‐induced contractions occurred in the presence of 20 mM‐procaine, while this agent completely blocked the contraction induced by caffeine. 6. Both GTP gamma S and InsP3 induced an increase in the Fura‐2 fluorescence signal of the bath medium surrounding the skinned MPA, indicating that GTP gamma S releases intracellular Ca2+. The release of Ca2+ induced by GTP gamma S was inhibited by GDP beta S. 7. During the initial phasic contraction induced by GTP gamma S, added InsP3 had little or no additive effect, in contrast to its additive effect during the latter sustained contraction induced by GTP gamma S.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of isoprenaline on cytosolic calcium concentrations and on tension in the porcine coronary artery.

“…(2) In smooth muscle, pharmacomechanical Ca2+ release is a major mechanism of excitation-contraction coupling (Somlyo, 1985). It is mediated by activation of the phospholipase C-inositol trisphosphate (1P,) cascade, coupled to receptors by G-proteins, and inhibitors of phospholipase C (neomycin) and of IP3 (heparin) block the release of intracellular Ca2+ induced by agonists, but not by caffeine (Kobayashi, Somlyo & Somlyo, 1988;Kobayashi, Kitazawa, Somlyo & Somlyo, 1989;Yamamoto, Kanaide & Nakamura, 1990). The present study showed (Fig.…”

Role of G‐proteins in muscarinic receptor inward and outward currents in rabbit jejunal smooth muscle.

“…As the depleting action of GTPyS was completely prevented by heparin (5 mg/ml), an obvious explanation is that GTPyS acts by increasing InsP3 production and that this occurs because GTPyS binds to a G-protein associated with PLC in the cell and in this way accelerates its activity. Thus GTPyS in jejunal cells does not seem to have any direct depleting action on the Ca store, as it does in permeabilized pulmonary artery smooth muscle strips (Kobayashi, Somlyo & Somlyo, 1988b).…”

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

“…The effect of GTPrS was preserved after blockade of IP3 receptors with heparin (14), elimination of Ca" stores with A23187 (15) or reduction of the stored Ca 21 with caffeine. Therefore, it is unlikely to be due to such an action of GTPrS on Ca2+ stores through an IP3 independent process as described for the pulmonary arteri al smooth muscle (12). The fact that GTPrS can cause depletion of Ca" stores exclusively through IP3 is demon strated by using Ca2+-activated K+ current as an indica for showing Ca 21 stores available for release in single volt age-clamped cells from rabbit jejunum (4).…”

“…The difference may arise by a slow diffusion of GTPrS from the patch pipette into the cell. In chemi cally-skinned arterial muscle strips, the GTPrS-induced Ca 2+ release has been reported to involve both IP3-de pendent and independent mechanisms (12).…”