EFFECTS OF ANTI PEPTIDE ANTIBODIES AGAINST THE 2ND EXTRACELLULAR LOOPOF HUMAN M2 MUSCARINIC ACETYLCHOLINE-RECEPTORS ON TRANSMEMBRANE POTENTIALS AND CURRENTS IN GUINEA-PIG VENTRICULAR MYOCYTES

The effects of anti-peptide antibodies against the second extracellula r loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using w hole-cell patch clamp technique. These effects were compared with thos e of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependen t manner. By using a ramp or step rectangular pulse protocol, it was f ound that the antibodies increased the outward K+ current and decrease d the inward basal I-Ca significantly. The reversal potential of both carbachol- and antibody-induced extra currents were close to -80 mV, b eing in proximity to the calculated E(k) of -90 mV. A beta-adrenergic receptor agonist, isoprenaline, prolonged the action potential and inc reased the overshoot which could be inhibited by both antibody and car bachol. Isoprenaline increased inward I-Ca and outward I-k simultaneou sly. Both antibody and carbachol could significantly reduce the isopre naline-stimulated I-Ca but not the isoprenaline-stimulated I-k. The an tibody- or carbachol-induced outward K+ current and the depressant eff ects of antibody and carbachol on isoprenaline-stimulated I-Ca were pa rtially antagonized by atropine. These results suggest that the anti-M 2 muscarinic receptor antibodies display a stimulatory activity simila r to muscarinic receptor agonist on the receptor-mediated electrophysi ological events.