CALCIUM CURRENTS AND CONTRACTION IN FROG ATRIAL TRABECULAE

The properties of two types of calcium current (I-Ca(T) and I-Ca(L) an d their relationship with contraction were studied in isolated frog at rial trabeculae using the double mannitol gap technique. In Ringer sol ution containing TTX the calcium currents observed are similar to the I-Ca(T) and I-Ca(L) found in single frog atrial cells. The results obt ained by using inorganic calcium channel blockers have shown that the phasic contraction appears only when I-Ca(T) and I-Ca(L) are simultane ously present. It is proposed that I-Ca(T) loads the sarcoplasmic reti culum (SR) while I-Ca(L)) triggers Ca2+ release from the SR.