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

抄録

1. Circular muscle strips of the guinea-pig gastric muscle produced spontaneous electrical activity in the form of slow waves. The slow wave amplitude, maximum rate of rise, duration, and frequency were 31 mV, 60 mV sec^-1, 4.3 sec, and 4.3 min^-1 on average, respectively. These parameters were not appreciably affected by 3μM nifedipine or nicardipine, even following membrane depolarization with 60mM K⁺.
2. Ni²⁺ (1-100μM) increased slow wave amplitude and frequency, but reduced the rate of rise, accompanied by membrane depolarization. The rate of rise and depolarization slowly 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 fundamentally 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 Co²⁺ greater than 1mM suppressed the slow waves. However, when the external Na⁺ was replaced with N-methyl-D-glucamine during the suppression, nearly normal electrical activity was resumed.
6. Since slow waves were not significantly affected by nifedipine (3μM) and Ni²⁺ (100 μM), 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 Ni²⁺ and Co²⁺ acting intracellularly. These ions at higher concentrations seem to inhibit the pacemaker activity more powerfully than they do the inward currents responsible for slow wave generation.