抄録
The effects of caffeine on mouse myometrium and guineapig ileal muscle were investigated by recording the contractile responseand the membrane activity with an intracellular microelectrode.
1) Caffeine in concentrations of 2 to 20mM suppressed the spontaneouscontraction of mouse myometrium. In the ileal muscle, low concentration (2 to 6 mM) caused an initial potentiation of contraction, then a resulting decay. With high concentration (20 mM), the dominanteffect was a relaxation. K contracture of both tissues was suppressedby all caffeine concentrations.
2) In mouse myometrium, caffeine caused a hyperpolarization, anincrease in membrane conductance and the suppression of spontaneousspike activity. With high concentration, the response evoked by externalcurrent stimulation became abortive.
3) The spike potential in the guinea pig ileal muscle had an amplitudeof about 30 to 50mV and was followed by positive afterpotential. Lowconcentration of caffeine accelerated the normal pattern spike discharge. With high concentration, the membrane was only slightly depolarized, but the frequency of spike discharge increased. The amplitude of spikepotential became larger, and the repolarization slower.
4) The different membrane responses to caffeine in mouse myometriumand guinea pig ileal muscle due to their dependence on the interactionbetween the membrane and Ca are discussed.
