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Alteration of the L‐type calcium current in guinea‐pig single ventricular myocytes by heptaminol hydrochloride

1 The effects of heptaminol on calcium current amplitude and characteristics were studied in single ventricular myocytes of guinea‐pig by use of the whole cell configuration of the patch clamp technique. 2 A concentration‐dependent decrease in ICa amplitude was observed. At heptaminol concentration as low as 10−6 m, this effect was observed in only two cells (n = 6). At 10−5 m the reduction of ICa was of 30 ± 15% (n = 11). 3 The current recovery from inactivation at — 40 mV holding potential (HP) seemed less sensitive to perfusion with heptaminol (> 10−6 m). However, at — 80 mV HP the overshoot of the recovery curve was decreased by heptaminol. 4 Both at — 40 mV and — 80 mV HP, heptaminol (10−5 m) significantly increased the steady state inactivation of ICa. 5 As previously proposed by others to explain the effects of membrane active substances, the effects of heptaminol may result from alterations in cell membrane properties and possibly from an increase in intracellular free calcium ion concentration.