Abstract: AIM: To examine the effects of propylene glycol mannate sulfate (PGMS)on the action potentials and contractile force in guinea pig papillary muscles. METHODS: An intracellular microelectrode was used to record fast (FAP)and slow (SAP) action potentials. RESULTS: PGMS concentration-dependently decreased the contractile force and the action potential duration (APD) of FAP without affecting the resting potential (RP), action potential amplitude (APA), and maximal upstroke velocity (V_max).The V_max, APA, and APD of BaCl₂-induced SAP were concentration-dependently decreased by PGMS and the effects were antagonized by isoprenaline.The APA and APD of isoprenaline-induced SAP were decreased by PGMS in a concentration-dependent manner and the effects were attenuated by elevation of intracellular Ca²⁺ concentration. CONCLUSLON: PGMS selectively inhibits the slow inward current.

Key words: pharmacology, polysaccharides, papillary muscles, action potentials, calcium channels, myocardial contraction, barium compounds, isoproterenol