LECTINS MODULATE CALCIUM CHANNELS IN CHICK SYMPATHETIC-GANGLIA

Calcium currents were measured in dissociated chick sympathetic ganglia using the whole cell patch-clamp technique. Lectins (1 mu M) were applied by local superfusion. All lectins tested reversibly inhibited Ca currents. Two types of inhibition were observed: a speeding up of inactivation and a voltage-dependent inhibition with slowing of the activation kinetics. When guanosine 5'-O-(3-thiotriphosphate) was substituted for guanosine triphosphate, the voltage-dependent inhibition was irreversible, while the acceleration of inactivation remained reversible. Guanosine 5'-O-(2-thiodiphosphate) suppressed the voltage-dependent inhibition, but had little effect on the speeding up of inactivation. Lectins with high affinities for alpha-L-fucose, N-acetylglucosamine or N-acetylgalactosamine preferentially induced a voltage-dependent inhibition, while lectins with or-D-galactose affinity produced an acceleration of inactivation. Lectins with D-mannose affinity produced both type of modulation. Differential effects of concanavalin-h and succinyl-Con-A indicate that the speeding up of inactivation may be due to cap formation. It is concluded that, depending on their carbohydrate specificity, some lectins activate G-protein-coupled receptors, and thereby inhibit calcium channels in a voltage-dependent manner. Other lectins speed up the inactivation of the same channels, possibly through a direct interaction.