EFFECTS OF LOBELINE ON SLOW ACTION-POTENTIAL AND FORCE OF CONTRACTION OF GUINEA-PIG PAPILLARY-MUSCLE

Intracellular microelectrode techniques were used to study the effects of N1-receptor agonist lobeline on the slow action potentials (SAP) and the force of contraction (FC), induced by histamine, BaCl2 and aminophylline, in catecholamine-depleted guinea pig papillary muscles in the presence of an M-cholinergic receptor antagonist atropine (3-mu-mol . L-1). In these preparations lobe-line (1-64-mu-mol . L-1) suppressed, in a dose-dependent manner, the action potential amplitude (APA), the action potential duration (APD), the maximal upstroke velocity (V(max)) and FC. Elevation of calcium concentration outside the myocardiac cells to 3.6 mmol . L-1 antagonized the effects of lobeline in different degrees. These results suggest that the lobeline inhibits the slow inward current I(si) of myocardiac cells.