The effect of taurine on the activation osmolality of the osmosensitive current in single ventricular myocytes of rabbits.

Abstract

An osmosensitive current was identified in rabbit ventricular cells and the effects of taurine on osmotic stress were examined. The osmosensitive current was measured with the whole-cell patch clamp technique and all known currents were blocked using Ba2+, Cd2+, Ni2+, diltiazem, ouabain, Cs+ and tetraethyl ammonium. When hyposmotic solution (200 mosmol/kg) was applied, the background current increased gradually. This osmosensitive current was dependent on Cl-. When the conductance of the activated current reached three times the control conductance, the osmolality was arbitrarily named the activation osmolality. The activation osmolality was regarded as an indication of cell volume expansion. With 20 mM taurine in the pipette solution, the activation osmolality was lowered significantly. With high [Na+] (32.5 mM) in the pipette solution, the effect of taurine in reducing the activation osmolality was larger than that in low [Na+] (2.5 mM). From these results, we conclude that taurine reduces the activation osmolality and this effect is more pronounced in the presence of high [Na+] in the pipette solution. It is suggested that Na+-dependent taurine transport could be involved in reducing osmotic stress.