Effects of atrial natriuretic peptide on abnormal automaticity of diseased human atrial muscles.

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A human atrial trabecula(0.8xl. 5mm)was dissected from a small piece of right atrial appendage excised from patients undergoing cardiac surgery. We first attempted to elucidate the ionic mechanisms for the low resting membrane potential(Vm)of human atrial preparations using double-barreled K^+- and Na^+-sensitive microelectrodes. Because various types of abnormal automaticities observed at a rate of about 70% in the ppecimens may be mainly caused by partial depolarizations of Vm. The intracellular K^+ activity(a^i_averaged 99.7<plus-minus>1.3mM(n=33), intracellular Na^+ activity(a^i_, 6.9<plus-minus>1.7mM(n=9)and Vm, 43.6<plus-minus>3.2(n=42). These findings suggest that the depolarization of Vm is neither due to a decrease in a^i_ nor an increase in a^i_ but probably due to a decrease in K^+ permeability for the membrane. We secondly examined the effects of atrial natriuretic peptide(ANP)on action potential characteristics and contractile tension of the human preparations. However, we found no significant effect of ANP on those parameters. So we intended to test the effects of ANP on the ionic current in single human atrial myocytes using whole cell voltage-clamp technique. However, there was only one isolated cell tolerable to do experiment among 31 human atrial tissues undergone cell-isolation procedures. Therefore, we could not obtain available informations about electrophysiologic effects of ANP on single human atrial cell, though we observed electrophysiologically reasonable actions of acetylcholine and nicorandil on it.