Effects of Endothelin-1 on Calcium and Potassium Currents in Guinea Pig Ventricular Cells

Abstract

内皮素(endothelin, ET-1)是由21個胺基酸組成的胜肽，能促使血管收縮、細胞分裂及心肌收縮。本研究利用傳統玻璃電極進行細胞内記錄來測試天竺鼠心室乳頭肌的動作電位、利用張力轉換來記錄乳頭肌收縮力；利用全細胞膜片箝(whole-cell patch clamp)技術來記錄酵素分離的單一心室肌細胞之鈣離子及鉀電流。10 nM ET-1的處理對乳頭肌的動作電位及其持續時間均沒有影響。但可迅速的、顯著的增加乳頭肌收縮力達原來的225％，收縮力在除ET-1清洗2分鐘後是能恢復的。10 nM ET-1的處理單一心室細胞可以抑制其向内L型鈣離子電流(I□, □)，此抑制的藥效很快，在處理3、6至9分鐘減少15、24、33％，處理12分鐘抑制才見漸平穩，以不含ET-1灌流液清洗20分鐘I□, □會有少許的恢復。藥物的處理使鈣離子電流高峰由膜電位0 mV轉至10 mV時。但ET-1對隨著時間增加的外向鉀離子電流(I[8e52])則沒有明顯的作用。此現象可推論ET-1增加乳頭肌收縮力，並非經由增加鈣離子向内流來引起作用的。

Endothelin-1 (ET-1), a 21 amino acid peptide, exerts a wide range of biological activities including vasoconstriction, mitogenesis, and inotropic effects on the heart. Action potential of guinea pig papillary muscle was recorded using traditioned microelectrode intracellular recording. The mechanical contractile force was recorded using a force-displacement transducer. The L-type calcium current (I□ [8ecf]) and time-dependent potassium current (I[8e52]) in isolated guinea pig ventricular cardiomyocytes were recorded by the whole-cell patch clamp technique. Endothelin-1 (10 nM) had no effect on amplitude and duration of treated papillary muscle action potential. The mechanical contractile force, however, was increased as much as 225%. This effect was reversible after 2 min washing in ET-1 free superfusate. Extracellular application of ET-1 significantly decreased peak amplitude of Ca²⁺ currents by 15±4%, 24±6%, 33+7% and 32±7% in ventricular myocytes after treatment for 3, 6, 9, and 12 min, respectively. The treatments also have a 10 mV shift in relationship to membrane potential. The effect was irreversible after washing for 20 min Endothelin-1 had no effect on the amplitude of I[8e52]. This indicated that the incremental contractile force in ET-1 treated papillary muscles was not by action of increasing I□ [8ecf].