Tetrodotoxin sensitivity of high K+-induced 86Rb efflux in the duodenal circular muscle of pigs.

The 86Rb efflux by high K+ was measured simultaneously during the mechanical responses in pig duodenal circular muscle using a superfusion technique. A slightly higher K+ (17.7-23.6 mM) simultaneously induced tetrodotoxin (TTX)-sensitive relaxation and 86Rb efflux. Much higher K+ (47.2-143.4 mM) contracted and also increased the 86Rb efflux markedly, but the extent of TTX-sensitive efflux remained the same as the one at 17.7-23.6 mM K+, indicating that the TTX-insensitive efflux was contraction-related. The former efflux may lead to hyperpolarization linked to relaxation.