Published Online
on November 11, 2002

A more recent version of this article appeared on December 10, 2002

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Submitted on June 24, 2002
Revised on August 29, 2002
Accepted on September 2, 2002

Nonselective Cation Currents Regulate Membrane Potential of Rabbit Coronary Arterial Cell. Modulation by Lysophosphatidylcholine

Kuniko Terasawa MD, Toshiaki Nakajima MD^*, Haruko Iida MD, Kuniaki Iwasawa MD, Hitoshi Oonuma MD, Taisuke Jo MD, Toshihiro Morita MD, Fumitaka Nakamura MD, Yoshiharu Fujimori MD, Teruhiko Toyo-oka MD, and Ryozo Nagai MD

From the Department of Cardiovascular Medicine (K.T., T.N., H.I., K.I., H.O., T.J., T.M., F.N., T.T., R.N.), University of Tokyo, Tokyo, Japan; and the Department of Cardiology (K.T., Y.F.), Narita Red Cross Hospital, Chiba, Japan.

^* To whom correspondence should be addressed. E-mail: masamasa{at}pb4.so-net.ne.jp.

Background—The effects of lysophosphatidylcholine (LPC) on electrophysiological activities and intracellular Ca²⁺ concentration ([Ca²⁺]_i) were investigated in coronary arterial smooth muscle cells (CASMCs).

Methods and Results—The patch clamp techniques and Ca²⁺ measurements were applied to cultured rabbit CASMCs. The membrane potential was -46.0±5.0 mV, and LPC depolarized it. Replacement of extracellular Na⁺ with NMDG⁺ hyperpolarized the membrane and antagonized the depolarizing effects of LPC. In Na⁺-, K⁺-, or Cs⁺-containing solution, the voltage-independent background current with reversal potential (E_r) of approximately +0 mV was observed. Removal of Cl^- failed to affect it. When extracellular cations were replaced by NMDG⁺, E_r was shifted to negative potentials. La³⁺ and Gd³⁺ abolished the background current, but nicardipine and verapamil did not inhibit it. In Na⁺-containing solution, LPC induced a voltage-independent current with E_r of approximately +0 mV concentration- dependently. Similar current was recorded in K⁺- and Cs⁺-containing solution. La³⁺ and Gd³⁺ inhibited LPC-induced current, but nicardipine and verapamil did not inhibit it. In cell-attached configurations, single-channel activities with single-channel conductance of 32pS were observed when patch pipettes were filled with LPC. LPC increased [Ca²⁺]_i as the result of Ca²⁺ influx, and La³⁺ completely antagonized it.

Conclusions—These results suggest that (1) nonselective cation current (I_NSC) contributes to form membrane potentials of CASMCs and (2) LPC activates I_NSC, resulting in an increase of [Ca²⁺]_i. Thus, LPC may affect CASMC tone under various pathophysiological conditions such as ischemia.

Key words: muscle, smooth • cells • ischemia • ion channels

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