Spike-free activation mechanism in smooth muscle of guinea pig stomach.

Electrical and mechanical activity of circular muscle strips of guinea-pigs stomach, taken from the distal corpus/proximal antrum region, were recorded. Spontaneous activity consisting of phasic contractions combined with bursts of spike potentials was suppressed by verapamil (5-10-6 - 2-10-5 mol/l). Under these conditions acetylcholine produced a spike-free tonic activation. Under normal conditions phasic contractions were superimposed on this tonic activation. The acetylcholine-induced activation, therefore, consists of two different components, one of which can be selectively blocked with verapamil. Both components disappear quickly in calcium-free solution. It can be concluded that two different calcium activation systems are responsible for the two components of activation. In comparative studies with taenia coli preparations a comparable spike-free tonic activation was not found.