L-palmitylcarnitine and calcium ions act similarly on excitatory ionic currents in avian ventricular muscle.
Palmitylcarnitine, an amphiphile that accumulates in and leaks from ischemic heart tissue, affected the fast sodium ion channel and the slow calcium channel in avian ventricular muscle. In the presence of 5.4 mM external potassium ion, palmitylcarnitine reduced the maximum rate of rise of the action potential and increased action potential duration at the plateau level without changing the resting potential. Steady state inactivation of the maximum rate of rise, an index of fast sodium ion current, was shifted by 3-6 mV to more positive potentials by palmitylcarnitine. Elevation of external calcium ion to 5.4 mM (normal = 1.8 mM), like palmitylcarnitine, reduced the maximum rate of rise and shifted the voltage at which the action potential was half maximum by 3 mV to more positive potentials without changing the resting potential. Elevated external calcium ion, unlike palmitylcarnitine, reduced the duration of action potentials initiated from a resting potential of -80 mV. Palmitylcarnitine and elevated external calcium ion increased the amplitude, the maximum rate of rise, and duration of calcium ion dependent action potentials recorded in the presence of 25 mM [K+]0 that completely inactivated the fast sodium ion channel. Steady state inactivation of the maximum rate of rise of calcium-dependent action potentials was consistently shifted to more positive potentials by palmitylcarnitine (3 mV) and by elevated external calcium ion (6 mV) when the initial external calcium ion was 0.9 mM. Palmitylcarnitine, like elevated calcium, evoked a positive inotropic effect in the presence of propranolol. The similarity of the effects of palmitylcarnitine (3 X 10(-5) to 3 X 10(-4)M) with those of elevated external calcium is consistent with the hypothesis that palmitylcarnitine, like elevated external calcium, influences sodium and calcium channel operation by an effect on membrane surface charge.