Characterization of the effects of AHN 086, an irreversible ligand of "peripheral" benzodiazepine receptors, on contraction in guinea-pig atrial and ileal longitudinal smooth muscle

The effects of AHN 086 and its reversibly acting structural analogue Ro 5-4864 were studied in the spontaneously beating guinea-pig atria and field-stimulated guinea-pig ileal longitudinal smooth muscle in the presence and absence of dihydropyridine calcium channel modulators. The treatment of guinea-pig atria with AHN 086 followed by extensive washing did not alter contraction. However, AHN 086 (0.5 microM) potentiated (88%) the positive inotropic responses by BAY K 8644, an effect that was not reversed by extensive washing of the tissue. Higher concentrations of AHN 086 (greater than 2 microM) irreversibly inhibited the intropic, but not the chronotropic responses to BAY K 8644, nifedipine, and isoproterenol. Ro 5-4864 (10 microM) produced a reversible enhancement of the inotropic responses and block of the chronotropic responses to BAY K 8644. In guinea-pig ileal longitudinal smooth muscle, both AHN 086 and Ro 5-4864 reversibly inhibited field-stimulated contractions. Neither Ro 5-4864 nor AHN 086 affected the ability of nifedipine to inhibit field-stimulated contractions of ileal longitudinal smooth muscle. Treatment of intact atrial with 5 microM AHN 086 followed by extensive washing resulted in a significant inhibition (30-50%) of 3H]Ro 5-4864 binding to peripheral benzodiazepine receptors and of 3H]nitrendipine binding to voltage-operated calcium channels, but did not affect 3H]dihydroalprenolol binding to beta-adrenergic receptors on atrial membranes. The same treatment applied to intact ileal longitudinal smooth muscle affected neither 3H] (-)-quinuclidinyl benzilate binding to muscarine receptors nor 3H]nitrendipine binding, but did result in a significant inhibition (30-50%) of 3H]Ro 5-4864 binding to ileal longitudinal smooth muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)