ATP DIRECTLY AFFECTS JUNCTIONAL CONDUCTANCE BETWEEN PAIRED VENTRICULAR MYOCYTES ISOLATED FROM GUINEA-PIG HEART

Effects of ATP on junctional conductance (g(j)) were investigated in paired ventricular myocytes isolated from guinea pig hearts. One cell of the pair was voltage-clamped with a single-patch pipette, and g(j) was measured after the perforation of the nonjunctional membrane of the partner cell. The current-voltage relation of g(j) was linear between -30 and +30 mV. The control g(j) at 5.0 mM ATP in 88 pairs of cells ranged from 100 to 1,055 nS (average, 268 nS). ATP within the range from 0.1 to 5.0 mM increased g(j) in a dose-dependent manner. The Hill coefficient was 2.6, and the half-maximum effective concentration of ATP was 0.68 mM. Adenylylimidodiphosphate (2 mM) caused a transient increase in g(j) in the presence of 0.5 mM ATP, but forskolin (30 μM), cyclic AMP (50 μM), catalytic subunit of cyclic AMP-dependent protein kinase (1 μM), and ADP (10 mM) had no significant effect on g(j). The temperature coefficient of g(j) in the presence of 5.0 mM ATP was 1.29. These findings suggest that g(j) in paired ventricular myocytes is directly regulated by ATP probably throug a specific ligand-receptor interaction between ATP and gap junctional channel protein.