[The ammonium chloride modification of the effect of sodium nitroprusside on the contractile activity of guinea pig papillary muscles]. / Modifikatsiia khloridom ammoniia vliianiia nitroprussida natriia na sokratitel'nuiu aktivnost' papilliarnykh myshts morskikh svinok.

The rise of intracellular pH (pH) caused by the replacement of 20 mM NaCl by NH4Cl was shown to enhance guinea-pig papillary muscle contractility while the pH decrease under the NH4Cl abolition from perfusion solution was obtained to reduce the contractile activity. Sodium nitroprusside (SN, 10 microM) does not influence the cardiac muscle contractility in controls but significantly decreases its levels under intracellular alkalinization. SN washout does not restore contractility, hence, the subsequent NH4Cl removal results in contractility increase. In most cases simultaneous action of SN and NH4Cl was accompanied by the development of cardiac mechanical instability. Thus, pHi change can provoke unexpected effects of nitrates.