Blockade by nickel ions of phasic contraction to K+ and high affinity calcium of ileal longitudinal muscle of guinea-pig

Abstract 1. Preincubation with 1 or 2mM Ni 2+ inhibited dose-dependently the ileal phasic response to K + (60 mM) without appreciable effects on the tonic response. Ni 2+ above 3mM inhibited the tonic response. 2. Ni 2+ inhibited the high affinity Ca 2+ sites than the low affinity sites during K + contraction. 3. After treatment with Ni 2+ , the K + response was fairly restored by a wash with normal medium. The nickel bound to the ileal cells was almost eliminated with the washing. 4. This probably indicates that Ni 2+ mainly inhibited the K + -induced phasic tension by reducing Ca 2+ release rather than Ca 2+ influx.