M.K. Mundey et al
Ileal contractions and m-opioid antagonists
901
morphine at 48C. Second, m-opioid responsive neurones in the
myenteric plexus (S neurones) are not aected by agents that
elevate cyclic AMP levels (Nemeth et al., 1986; Johnson &
Pillai, 1990).
the absence of an agonist. While dierences between the
antagonists were noted, it seems likely these are a consequence
of non-opioid actions rather than evidence for partial inverse
agonism at a constitutively-activated receptor.
In summary, we have demonstrated that overnight exposure
of the guinea-pig isolated ileum to morphine induces changes
in myenteric m-opioid receptors, qualitatively similar to those
reported in SH-SY5Y and HEK 293 cells (Wang et al., 1994;
1999), that permit antagonists to elicit a biological response in
MKM was supported by the BBSRC (ROPA Award) and we are
grateful to Dr Steve Alexander for his helpful advice during the
preparation of the manuscript.
References
AMMER, H. & SCHULZ, R. (1993). Alteration in the expression of G-
proteins and regulation of adenylate cyclase in human neuro-
blastoma SH-SY5Y cells chronically exposed to low-ecacy m-
opioids. Biochem. J., 280, 512 ± 520.
JANSSON, C.C., KUKKONEN, J.P., NASMAN, HUIFANG, G.E.,
WURSTER, S., VIRATANEN, R., SAVOLA, J.-M, COCKCROFT, V.
& AKERMAN, K.E.O. (1998). Protean agonism at a2-adrenocep-
tors. Mol. Pharmacol., 53, 963 ± 968.
AMMER, H. & SCHULZ, R. (1997). Chronic morphine treatment
increases stimulatory Beta-2 adrenoceptor signaling in A431 cells
stably expressing the Mu opioid receptor. J. Pharmacol., Exp.
Ther., 280, 512 ± 520.
JOHNSON, S.M. & PILLAI, N.P. (1990). Hyperpolarization of
myenteric neurones by opioids does not involve cyclic adenosine
3',5'-monophosphate. Neurosci., 36, 299 ± 304.
JOHNSON, S.M., WILLIAMS, J.T., COSTA, M. & FURNESS, J.B. (1987).
Naloxone-induced depolarization and synaptic activation of
myenteric neurons in morphine-dependent guinea-pig ileum.
Neurosci., 21, 595 ± 602.
KENAKIN, T. (1999). Ecacy in drug receptor theory: outdated
concept or undervalued tool?. Trends Pharmacol Sci., 20, 400 ±
405.
KISHIOKI, S., INOUE, N., NISHIDA, S., FUKUNAGA, Y. & YAMA-
MOTO, H. (1995). No relation of plasma morphine levels to the
severity of naloxone-induced withdrawal in acute morphine-
dependent rats. Jap. J. Pharmacol., 69, 187 ± 193.
AVIDOR-REISS, T., BAYEWITCH, M., LEVY, R., MATUS-LEIBO-
& VOGEL, Z. (1995). Adenylyl cyclase
VITCH, N., NEVO, I.
supersensitization in m-opioid receptor-transfected Chinese
Hamster Ovary cells following chronic opioid treatment. J. Biol.
Chem., 270, 29732 ± 29738.
BILSKY, E.J., BERNSTEIN, R.N., WANG, Z., SADEE, W. & PORRECA,
F. (1996). Eects of naloxone and D-Phe-Cys-Tyr-D-Trp-Arg-
Thr-Pen-Thr-NH2 and the protein kinase inhibitors H7 and H8
on acute morphine dependence and antinociceptive tolerance in
mice. J. Pharmacol. Exp. Ther., 277, 484 ± 490.
BURFORD, N., WANG, D. & SADEE, W. (2000). G-protein coupling of
m-opioid receptors (OP3): elevated basal signalling activity.
Biochem. J., 348, 531 ± 537.
KRAMER, T.C., SHOOK, J.E., KAZMIERSKI, W., AYRES, E.A., WIRE,
W.S., HRUBY, V.J. & BURKS, T.F. (1989). Novel peptidic Mu
opioid antagonists: pharmacologic characterization in vitro and
in vivo. J. Pharmacol. Exp. Ther., 249, 544 ± 551.
CHAKRABARTI, S., RIVERA, M., YAN, S.-Z., TANG, W.-J.
&
GINTZLER, A.R. (1998). Chronic morphine augments Gbg/GSa
stimulation of adenylyl cyclase: relevance to opioid tolerance.
Mol. Pharmacol., 54, 655 ± 662.
MALDONADO, R., NEGUS, S. & KOOB, G.F. (1992). Precipitation of
morphine withdrawal syndrome in rats by administration of mu-,
delta-, and kappa-selective opioid antagonists. Neuropharmacol.,
31, 1231 ± 1242.
MILLER, L., SHAW, J.S. & WHITING, E.M. (1986). The contribution
of intrinsic activity to the action of opioids in vitro. Br. J.
Pharmacol., 87, 595 ± 601.
MILLIGAN, G., BOND, R.A. & LEE, M. (1995). Inverse agonism:
pharmacological curiosity or potential therapeutic strategy.
Trends Pharmacol. Sci., 16, 10 ± 13.
CHIDAC, P., NOUET, S. & BOUVIER, M. (1996). Agonist-induced
modulation of inverse agonist ecacy at the b2-adrenergic
receptor. Mol. Pharmacol., 50, 662 ± 669.
COLLIER, H.O.J., CUTHBERT, N.J. & FRANCIS, D.L. (1981). Model of
opiate dependence in the guinea-pig ileum. Nature, 302, 618 ±
621.
CONNOR, M., INGRAM, S.L. & CHRISTIE, M.J. (1997a). Cortistatin
increase of a potassium conductance in rat locus coeruleus in
vitro. Br. J. Pharmacol., 122, 1567 ± 1572.
CONNOR, M., YEO, A. & HENDERSON, G. (1997b). Neuropeptide Y
Y2 receptor and somatostatin sst2 receptor coupling to mobiliza-
tion of intracellular calcium in SH-SY5Y human neuroblastoma
cells. Br. J. Pharmacol., 120, 455 ± 463.
MUNDEY, M.K., MASON, R.
& WILSON, V.G. (1998). Selective
potentiation by ouabain of naloxone-induced withdrawal con-
tractions of isolated guinea-pig ileum following exposure to
morphine. Br. J. Pharmacol., 124, 911 ± 916.
NEMETH, P.R., PALMER, J.M., WOOD, J.D. & ZAFIROV, D.H. (1986).
Eects of forskolin on electrical behaviour of myenteric neurones
in guinea-pig small intestines. J. Physiol., 376, 439 ± 450.
NESTLER, E.J. (1992). Molecular mechanisms of drug action. J.
Neurosci., 12, 2439 ± 2450.
COSTA, T. & HERZ, A. (1989). Antagonists with negative intrinsic
activity at d-opioid receptors coupled to GTP-binding proteins.
Proc. Natl. Acad. Sci. U.S.A., 86, 7321 ± 7325.
DAVID, C., DAVIS, N., MASON, R. & WILSON, V.G. (1993). Evidence
for functional dissociation of dependence and tolerance in
guinea-pig isolated ileal segments following 20 hours exposure
to morphine in vitro. Br. J. Pharmacol., 110, 1522 ± 1526.
DELEAN, A., MUNSON, P.J. & RODBARD, D. (1978). Simultaneous
analysis of families of sigmoidal curves: applications to bioassay,
radioligand assay and physiological dose response curves. Am. J.
Physiol., 235, E97 ± E102.
PORTOGHESE, P.S., LIPKOWSKI, A.W. & TAKEMORI, A.E. (1987).
Binaltorphimine and nor-binaltorphimine, potent and selective
k-opioid receptor antagonists. Life Sci., 40, 1287 ± 1292.
STANDIFER, K.M., CHENG, J., BROOKS, A.I., HONRADO, C.P., SU,
W., VISCONTI, L.M., BIEDLER, J.L. & PASTERNAK, G.W. (1994).
Biochemical and pharmacological characterization of Mu, Delta
and Kappa3 opioid receptors expressed in BE(2)-C neuroblasto-
ma. J. Pharmacol. Exp. Ther., 270, 1246 ± 1255.
DHAWAN, B.N., CESSELIN, F., RAGHUBIR, R., REISINE, T.,
& HAMON, M. (1996).
TONINI, M., FIORI, E., BALESTRA, B., SPELTA, V., D'AGOSTINO, G.,
DI NUCCI, A., BRECHA, N.C. & STERNINI, C. (1998). Endomor-
phin-1 and Endomorphin-2 activate m-opioid receptors in
myenteric neurons of the guinea-pig small intestines. Naunyn
Schmiedeberg's Arch. Pharmacol., 358, 686 ± 689.
BRADLEY, P.B., PORTOGHESE, P.S.
International Union of Pharmacology, XII. Classi®cation of
opioid receptors. Pharmacol Rev., 48, 567 ± 592.
FENUIK, W., DIMECH, J., JARVIE, E.M. & HUMPHREY, P.P.A. (1995).
Further evidence from functional studies for somatostatin
receptor heterogeneity in guinea-pig isolated ileum, vas deferens
and right atrium. Br. J. Pharmacol., 115, 975 ± 980.
HAWKINS, K.N., KNAPP, R.J., LUI, G.K., GULYA, K., KAZMIERSKI,
W., WAN, Y.-P., PELTON, J.T., HRUBY, V.J. & YAMAMURA, H.I.
(1989). [3H]-[H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2]
([3H]CTOP), a potent and highly selective peptide for Mu opioid
receptors in rat brains. J. Pharmacol. Exp. Ther., 248, 73 ± 80.
WANG, Z., BILSKY, E.J., PORRECA, F.
&
SADEE, W. (1994).
regulatory
Constitutive m-opioid receptor activation as
a
mechanism underlying narcotic tolerance and dependence. Life
Sci., 54, PL339 ± PL350.
WANG, Z., BILSKY, E.J., WANG, D., PORECCA, F. & SADEE, W.
(1999). 3-Isobutyl-1-methylxanthine inhibits basal m-opioid
receptor phosphorylation and reverses acute morphine tolerance
and dependence in mice. Eur. J. Pharmacol., 371, 1 ± 9.
British Journal of Pharmacology, vol 131 (5)