Effect of tinctormine on contraction and Ca²⁺ currents in single cardiac myocytes from dog

Effect of tinctormine (TIN) on the contractile response and Ca2+ currents (lea) were investigated in dispersed single canine ventricular myocytes. Contraction were measured by a video-edge detector and Ca2+ currents were recorded using the whole-cell voltage clamp technique. TIN in low concentrations (10−7M) selectively reduced the contractile response in single ventricular cells by 50% of the control without affecting Ica. These inhibitory effects of the contractile response showed concentration-dependency and were reversible. However, TIN in high concentrations (10−5M) reduced the peak Ca2+ currents by 42% of the controls and completely inhibited the contractile response in single myocytes. These inhibitory effects on lea were concentration-dependent. These results assumed that tinctormine exerts a negative inotropic effect which is mediated in part through reduction of the peak Ca2+ currents and possibly also due to inhibition of the Na+-Ca2+ exchange process and/or inhibition of the Ca2+ release from the sarcoplasmic reticulum (SR). © 1994, Gustav Fischer Verlag · Stuttgart · Jena · New York. All rights reserved.