The aim of the study was to investigate the effects of 2-aminopyridine (2-AP) and its new sulfonylcarbamide derivatives AP21, AP22, AP26, and AP27 (10(-(5))-10(-(3)) M) on pinacidil (5x10(-(5)) M), an activator of K(ATP) channels, induced shortening of action potential duration and reduction of contraction force in guinea pig papillary muscles. Experiments were carried out using a standard method of myocardium electromechanical activity registration. Under control conditions (perfusion of papillary muscles with Tyrode solution), an average of action potential duration (APD), measured at 90% (APD(90)) and 50% (APD(50)) of repolarization, were 211.78+/-8.6 ms and 173.22+/-8.3 ms (n=18), respectively, and contraction force was 1.77+/-0.36 mN (n=18). Pinacidil markedly decreased APD(90) to 58.16+/-4.4%, APD(50) - to 52.51+/-4.85% (n=18), and contraction force - to 30.45+/-4.06% (n=18), (p<0.001) vs. control. 2-aminopyridine and its sulfonylcarbamide derivative AP22 (with 4-toluolsulfonylcarbamide fragment and methyl iodide-quaternized nitrogen of the pyridine ring) had no effect on the pinacidil-induced shortening of action potential and reduction of contraction force. 2-aminopyridine derivatives, AP21 (with 4-toluolsulfonylcarbamide fragment) and AP26 (with allyl bromide-quaternized nitrogen of the pyridine ring), showed a weak effect on pinacidil-induced shortening of action potential duration. The 2-aminopyridine derivative AP27 (with the 4-toluolsulfonylcarbamide fragment where nitrogen of the pyridine ring was quaternized by 4-nitrobenzyl bromide) had the most potent stimulatory effect on action potential duration and contraction force, which were reduced by pinacidil.