The whole-cell voltage-clamp technique was applied to isolated ventricular myocytes to investigate the effects of extracellular and intracellular zinc application on L-type Ca2+ channel currents (ICa). Extracellular zinc exposure at micromolar concentration induced a reversible (with washout of ZnCl2) reduction (30%) of ICa with no change in current-voltage relationship. On the other hand, an increase of intracellular free-zinc concentration, [Zn2+]i, from normal (less than 1 nM) to approx 7 nM with 10 microM Zn-pyrithione exposure caused an inhibition of 33+/-6% in the peak of the ICa and altered the voltage dependency of L-type Ca2+ channels with a 10-mV left shift and a hump at around -40 mV in its current-voltage relation. In contrast, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) strongly inhibited the ICa (42+/-2%), with only a small but detectable outward shift of the holding current measured at the end of the pulses. Zn-pyrithione and TPEN caused a reproducible decrease of the ICa. Interestingly, TPEN application, without Zn-pyrithione pretreatment, inhibited the ICa (35+/-2%) with no change in voltage dependency. Taken together, the results suggest that both extracellular and intracellular zinc increases under pathological conditions in cardiomyocytes can alter the ICa, but their effects are not in the same order and same manner. One should consider these possible side effects when it is suggested to be vital to cardiovascular cell integrity and functions.