Fig. 1. T- and L-type calcium currents in isolated guinea pig atrial myocyte. L-type Ca²⁺currents were activated by depolarizing voltage pulses from holding potentials (HP) of −50 (A ) and −90 mV (B ). (C ) Differences obtained by subtracting currents elicited from HP −50 mV from currents elicited from HP −90 mV. (Top ) Current traces recorded at test potential of −30 and +10 mV. (Bottom ) Corresponding current–voltage (I-V) values of peak currents elicited from HP −90 and HP −50 mV and the subtracted I-V representing T-type current. The slow inactivating current, representing the L-type channel, peaked at +10 to +20 mV, whereas the fast decaying inward current peaked at −30 mV is indicative of T-type calcium current. The arrows indicate zero-current levels.