REGULATION OF CARDIAC GAP JUNCTION CHANNEL PERMEABILITY AND CONDUCTANCE BY SEVERAL PHOSPHORYLATING CONDITIONS

Short term (15 min) effects of activators of protein kinase A (PKA), P KC and PKG on cardiac macroscopic (g(j)) and single channel (y(j)) gap junctional conductances were studied in pairs of neonatal rat cardiom yocytes. Under dual whole-cell voltage-clamp, PKC activation by 100 nM TPA increased g(j) by 16 +/- 2% (mean +/- S.E.M., n=9), 1.5 mM of the PKG activator 8-bromo-cGMP (8Br-cGMP) decreased g(j) by 26 +/- 2% (n= 4), whereas 1.5 mM of the PKA activator 8Br-cAMP did not affect g(j) ( 1 +/- 5%, n=11). Single cardiac gap junction channel events, resolved in the presence of heptanol, indicated two y(j) sizes of 20 pS and 40- 45 pS. Under control conditions, the larger events were most frequentl y observed. Whereas 8Br-cAMP did not change this distribution, TPA or 8Br-cGMP shifted the y(j) distribution to the lower sizes. Diffusion o f 6-carboxyfluorescein (6-CF), a gap junction permeant tracer, from th e injected cell to neighboring cells was studied on small clusters of neonatal rat cardiomyocytes. Under control conditions, 6-CF labeled 8. 4 +/- 0.4 cells (mean +/- S.E.M., n=31). Whereas 8Br-cAMP did not chan ge the extent of dye transfer (8.1 +/- 0.5 cells, n=10), TPA restricte d the diffusion of 6-CF to 2.2 +/- 0.2 cells (n=30) and 8Br-cGMP to 3. 5 +/- 0.3 cells (n=10). This suggests that permeability and single cha nnel conductance of Cx43 gap junction channels are parallel related. A ltogether, these results point to the differential modulation of elect rical and metabolic coupling of cardiac cells by Various phosphorylati ng conditions.