TheEffects of Nickel and Cobalt Ions Electrical Activity , Slow Wave , in the Guinea - pig Gastric Antrum the on the Spontaneous Circular Muscle of

l, Circular muscle strips of the guinea-pig gastric muscle produced spontaneous electrical activity in the forrn of slow waves. The slow wave amplitude, maxiinum rate of rise, duration, and frequency were 31 mV, 60mVsec'i, 4.3sec, and 4.3minmi on average, respectively. These parameters were not appreciably affected by 3#M nifedipine or nicardipine, even followihg rnernbrane depolarization with 60 mM K'. 2. Ni2' {1-100 ptM) increased slow wave amplitude ancl frequency, but reduced the rate of rise, accompanied by rnembrane depolarization. The rate of rise and deporarization slewly recovered to the control values in the continuous presence of Ni2', but slow wave frequency remained high. The recovery after wash-out was very poor particularly when a high concentration of Ni2' was applied. 3. The effects of Co2' were fundarnentally the same as those of Ni2". 4. Removal of external Ca2' slowly reduced the rate of rise and amplitude of the slow waves in the absence and the presence of Ni2' and Co2', although the effects were reduced in the presence of these metal ions. 5. Concentrations of Ni2' and Ce2' greater than 1mM suppressed the slow waves. However, when the external Na' was replaced with N-methy]-D-glucamine during the suppression, nearly normal electrical activity was resumecl. 6. Since slow waves were not significantly affected by nifedipine (3 "M) and Ni2' (100 "M), the inward currents generating slow waves do not seem to flow through L-type Ca2' channels or typical T-type Ca2' channels. Slow waves are probably potentiated by NiZ' and Co2' acting intracellularly. These ions at higher concentrations seem to inhibit he pacemaker activity more powerfully than they do the Inward currents responsible for slow wave generatlen.