Spontaneous tension oscillations in guinea-pig atrial trabeculae.

Spontaneous tension oscillations have been recorded from intact guinea-pig auricular trabeculae bathed in Na-poor and/or Ca-rich solutions. The frequency of these oscillations and that of after-contractions (oscillations following an electrically induced contraction) evoked under identical experimental conditions was the same (33 degrees C). The amplitude of the oscillations rose when the [Ca2+]0/[Na+]0(2)-ratio or the intracellular Na-concentration was increased. When the increase of the [Ca2+]0/[Na+]0(2)-ratio was relatively small, tension oscillations only occured after a period of electrical stimulation. The oscillation-frequency increased slightly in media containing 70 instead of 5.4 mM KCl. MnCl2 (3 mM) did not affect either the amplitude or the frequency of the oscillations. Caffeine (0.5-2.5 mM) decreased the amplitude and enhanced the frequency of the oscillations. After-contractions were diminished and, at higher concentrations, abolished. It is demonstrated that the membrane potential does not participate in the process causing the tension oscillations. An increased [Ca2+]i is a prerequisite for the occurrence of these oscillations. Characteristics of intracellular Ca-movement probably determine the amplitude and frequency of the spontaneous oscillations of tension.