Effects of Irradiation with Low-energy X-rays on Resting- and Action-potentials of Skeletal- and Heart-muscle Fibres

Summary

The effects of x-irradiation (50 kv) on resting- and action-potentials of isolated frog sartorius muscles, of heart-muscle fibres (papillary muscles of cats and Purkinje fibres of calves and sheep) were investigated by the intracellular recording technique. On frog sartorius fibres, radiation doses below 160 kr had no effect on the resting-potential; higher doses led to a dose-dependent decrease of about 1 mv per 160 kr. This effect was independent of the dose-rate in a range from 3 up to 85 kr/min. Shape and amplitude of the action-potential of frog sartorius fibres (stimulus frequency: 0·2/min) were not influenced significantly by irradiation of 15 min duration up to doses of 600 kr.

On rhythmically-stimulated (85/min), isolated papillary muscles, irradiation with total doses up to 240 kr had no effect on the resting- and action-potential. Higher doses (345–440 kr) produced a significant fall in the resting-potential, action-potential and rate of rise, as well as a shortening of repolarization-time and a decrease in mechanical tension. These changes were most marked immediately after irradiation and were partly reversible within one hour. Spontaneously-beating Purkinje fibres were at least 10–15 times more sensitive to x-rays than papillary muscles. As in papillary muscle, irradiation caused a decrease in the maximal diastolic potential, the action-potential and the upstroke velocity, the latter effect being most pronounced. At the same time, some decrease in slow diastolic depolarization and frequency was observed. All these changes were reversible within 30 min. The observed effects point to a partial inactivation of the sodium-carrying system as a possible primary mechanism of action.