Electrophysiological effects of acetyl glyceryl ether phosphorylcholine on cardiac tissues: comparison with lysophosphatidylcholine and long chain acyl carnitine.

Electrophysiological effects of synthetic platelet activating factor, acetyl glyceryl ether phosphorylcholine (AGEPC), were examined and compared with those of lysophosphatidylcholine (LPC) and long chain acyl carnitine (AC) in canine Purkinje fibres and guinea-pig papillary muscles, by use of standard microelectrode techniques. In canine Purkinje fibres, AGEPC at concentrations higher than 3 X 10(-5)M, decreased maximum diastolic potential, action potential amplitude and the maximum upstroke velocity of phase 0. AGEPC also induced abnormal automaticity arising from depolarized membrane potentials. LPC and AC in concentrations higher than 3 X 10(-5)M also produced virtually identical electrophysiological alterations in Purkinje fibres. Although twitch tension was slightly decreased by low concentrations (10(-6)-10(-5)M) of these amphiphilic lipids, a transient positive inotropic response appeared at the beginning of a progressive depolarization after exposure to higher concentrations of the amphiphiles. In guinea-pig papillary muscles, AGEPC in concentrations higher than 3 X 10(-5)M produced slight decreases in resting membrane potential, action potential amplitude and action potential durations, concomitantly with a positive inotropic response. These electrophysiological and mechanical changes were also induced by LPC and AC at comparable concentrations. In guinea-pig papillary muscles depolarized with 25 mM [K+]0, AGEPC, LPC and AC all evoked slow action potentials at a concentration of 10(-4)M. It is concluded that in isolated cardiac tissues AGEPC exerts electrophysiological effects similar to those of LPC and AC only at high concentrations, and that the non-specific interaction of amphiphiles with sarcolemmal membrane may be responsible for the electrophysiological and mechanical effects.